Looking through Yahoogroups, I came up with the following lists for 
specific IALs, which some here may want to look at. To access a list, 
simply attach the name I give here to the prefix . The first number is the number of 
subscribers to the list (this is probably misleading for at least the 
Esperanto and Interlingua lists, since both are mirrors, the 
Esperanto list of the newsgroup soc.culture.esperanto and the 
Interlingua list of the real list "interlng" which is hosted by a 
university server somewhere or other). The second number is the 
number of articles posted to the list so far in 2007 (which should be 
less misleading, assuming the mirror lists are working properly). For 
most, though not all, of these lists the archives are public.

Volapuk              volapuk            175    39
Esperanto            esperanto-l        229  1977
Latino sine Flexione europeano          129     0
Ido                  idolisto           225   325
Adjuvilo             adjuvilo            13    25
Interlingue          occidental         118   343
Novial               novial-discussion   30   103
Interlingua          interlng           100   676
Folkspraak           folkspraak         347   683
Lingua Franca Nova   LinguaFrancaNova   181    90
Klingon              Klingon_Language   157    40
Toki Pona            tokipona           296  1129

Some comments on these various lists:

(1) Volapuk. The one message in May so far was a "New file uploaded 
to" advisement, in English (of course); of the four messages in 
April, three had to do with Jim Henry's interview with Andrew 
Drummond, the author of the novel "[A Handbook of] Volapuk" and one 
was another "New file uploaded to" advisement, all of them in English.

(2) Esperanto. There are other Yahoo Esperanto lists (hundreds of 
them, actually, and it sometimes seems as though I subscribe to all 
of them, though actually my subscription list is fewer than 100, I 
think; latest is the list for the Esperanto group in Queretaro, 
Mexico). Most of the postings are in Esperanto, though occasionally 
you'll get an English posting (and, I think, even a spam every now and then).

(3) Latino sine Flexione. I can't look at the archives on this list, 
because they're private, but it really doesn't matter -- the last 
message was posted in June, 2006, one of two for the entire year of 
2006 and one of only 20 since the list was created in mid-2002.

(4) Ido. If I'm not mistaken, there are also a number of other Ido 
lists. Searching on "Ido" I got 159 responses, but most of these were 
spurious; but I hit enough genuine Ido lists in the first 30 to 
suggest that there might be between 10 and 20 Ido lists at Yahoo. My 
favorite, of the ones I saw, has to be Bebson Hochfeld's and Jean 
Martignon's "idolerneyo", to participate in which "onu devas per sua 
honoro jurar ke lu ne esas un de sinistrani od fashisti ..." If I had 
any honor, I think I'd lose out on one of these. All the postings of 
the last 30 (out of 65 in May so far) appear to be in Ido.

(5) Adjuvilo. What can one say? Of the last 30 postings, *every 
single one* appears to be a spam message. I would say that this list 
is basically moribund.

(6) Interlingue. Searching on "Occidental" is a good way to get 
frustrated, the word is so common in list descriptions. Searching on 
"Interlingue" gave me the lists "interlingue" and "kosmoglott" with 
one member each (anybody care to guess who?) and no messages, the 
list "Interlingue_Rome_2004" which has nothing to do with 
Interlingue/Occidental, and finally the "occidental" list. Of the 
last 30 postings on the list (all in May, which has had 49 postings 
so far), most seem to be in Occidental, and -- surprise, surprise! -- 
a majority come not from Bob Petry (aulinuniv), though he posts 
there, but from other legitimate posters, including several Auxlangers.

(7) Novial. There's also a list with the more appropriate name 
"novial", but it has fewer subscribers, and the 26 masochists who 
have maintained their subscriptions have been subjected to an 
unbroken diet of spam since September, 2005 (that's assuming that the 
subscriptions don't themselves all belong to spammers). So the 
Novialists are stuck with "novial-discussion". Of the latest 30 
postings (out of 56 so far this month), all but one are in English 
rather than Novial (the exception is from our own Don G who seems to 
be well acquainted with a huge number of conlangs, including the 
numerical "Timerio").

(8) Interlingua. A search on "Interlingua" gives 46 lists, of which 
more than half are spurious; but I hit enough genuine Interlingua 
lists in the first 10 to suggest that, as with Ido, there may be 
10-20 Interlingua lists at Yahoogroups. You may wish to look for 
yourself. Of the latest 30 postings (out of 97 so far in May), all 
are in Interlingua.

(9) Folkspraak. There's another group, "Folksprak", with five members 
and seven messages in the year it's been around; evidently the 
creator of the list didn't know how to spell the name of the language 
(or perhaps he's using a different dialect). In the "folkspraak" 
list, of the latest 30 postings (which go back to March, there having 
been only eight in May so far), once you throw out the 10-20% that 
are spams, the rest are all in English.

(10) Lingua Franca Nova. Of the latest 30 postings (which also go 
back to March, there having been a total of 11 in May so far), all 
are in Lingua Franca Nova.

(11) Klingon. There appear to be several lists devoted to the Klingon 
language, but this is the largest by far. Of the latest 30 postings 
(which go back to January, there having been only one in May so far), 
every single one is in English; there are no Klingon postings.

(12) Toki Pona. The number of subscribers and messages comes as a 
surprise to me. Of the latest 30 postings (out of 386 in May so far) 
four are in Esperanto, several (I stopped counting) in Toki Pona, and 
probably a majority in English.

It looks to me as though users of Esperanto, Ido, Interlingua, Lingua 
Franca Nova and, to a great extent, Occidental take their languages 
seriously, at least in their mailing lists. Users of Toki Pona seem 
hesitant about this (but then Toki Pona was never really intended to 
be taken seriously, though I'm sure its creator, like Diego Marani of 
Europanto, would be more than pleased if it was). Users of Volapuk, 
Novial, Folkspraak and Klingon seem not to be very serious about 
their languages *qua* languages. Users of Latino sine Flexione and 
Adjuvilo, by the evidence of their lists, seem to be non-existent.

Opinions (in English):
Esperanto (in English):
Literaturo (Esperante):