The OCaml community doesn't have anybody who promotes the language with quite as much gusto as dons, to my knowledge, and its library situation is a bit messy - there are nonstandard community replacements for the standard library[1] because Inria is just not going to fix some major warts. It has libraries[2] (and a pretty good library manager[3]), but OCaml has been around for quite a while and hasn't ever seemed to aquire critical mass. That degree of blatant fragmentation probably makes people wary.
Haskell seems to be stealing its thunder now. There are numerous "intro to Haskell" / monad tutorial / etc. articles out there, and the OCaml community seems very quiet, by comparison. I don't particularly care for Haskell* , but its designers and users have done a good job of ensuring people hear about it, and get at least a roughly accurate first impression of what makes it noteworthy.
* I don't like laziness as a default, I've been burned a couple times by portability issues (and the way that "whatever GHC does right now" has become a de-facto standard means that portability issues are probably not a priority), and it's academia-centric "avoid success at all costs" attitude doesn't sit right with me.
I, for one, adore the "avoid success at all costs" attitude
The trappings of success for programming languages are pain and suffering, having your community inundated with incurious idiots, losing the ability to do anything new and cool because you have to maintain stability for the horde.
Witness Alan Kay's experience with Smalltalk -- he was forced to fork himself and start over every time he succeeded in getting users.
It's a great stance for a language that focusing primarily on research and innovation, but it does put a damper on getting things done sometimes. Some stability and concessions to practicality go a long way.
I think that having a clean break at major revisions (e.g. Python 3, Lua 4.0 to Lua 5.0) and cleaning up cruft is probably a reasonable approach, as long as it's handled carefully and half the community doesn't stay with the old version. (It was easier with Lua because it's so small, and usually embedded in something else.)
"I've been burned a couple times by portability issues (and the way that "whatever GHC does right now" has become a de-facto standard means that portability issues are probably not a priority)"
I am interested in this issue and would love to hear more details. Portability between different Haskell implementations or portability of GHC to different operating systems?
In the early years of Haskell there were a number of implementations experimenting with different things, and eventually the surviving ones converged on a standard -- Haskell 98.
Since then (especially in the last 5 years), the GHC community has been regularly releasing all sorts of shiny new toys -- obviously introducing features unsupported by other implementations, but also frequently breaking compatibility with their own previous implementations. OS portability has not been much of an issue.
Haskell Prime is an effort underway by the GHC guys to not only define a new set of standard libraries, but to make Python3000-style purposefully incompatible changes to the core language. This is hoped to become a new standard, Haskell 2010.
I should preface this by noting that I haven't looked into the situation recently, and the problem may have been fixed, but it really soured me on Haskell. (At a glance, it looks the same, and discussions with a presenter at a local barcamp implied no real change.) I stopped worrying about it because I'm quite content with Lua for small personal projects, and OCaml and Erlang seem to be more my style than Haskell for larger ones.
So, that said: I primarily use OpenBSD and FreeBSD, and bootstrapping recent versions of GHC from source has been broken for a long time. OpenBSD's current GHC is 6.6.1, and FreeBSD's is 6.8.x, but (last time I checked) was marked as broken. While porting language runtimes to OpenBSD can be tricky due to e.g. its randomized malloc, an open-source language that doesn't even build from source on FreeBSD probably doesn't place much of a priority on portability. GHC 6.6.1's ghci segfaults on my openbsd/amd64 system, too.
Just after I got settled with XMonad, GHC updated without a clear plan for source bootstrapping. I get the impression that a lot of people just use Debian/Arch/etc., like dons did[1]. (I'm a (somewhat minor) OpenBSD porter, so I probably care about this more than many people.)
Here's a Hackage bug ticket, closed after a year and a half with the note that they're probably just not going to support building that way anymore:(http://hackage.haskell.org/trac/ghc/ticket/1346). It's not hard to find griping about the situation on the openbsd-ports list.
While GHC is just one compiler (and I've put some time into helping with updating Common Lisp and Scheme ports in the past, due to similar issues), Haskell programmers seem to assume a recent version of GHC and its extensions, making "whatever GHC does" a de-facto standard. That rules it out for me entirely, and I wonder if anybody else feels the same.
What's also weird is that OCaml doesn't even have a big following in France, the French are well-known for championing their own ideas in the face of whatever Les Rosbifs are doing.
I get the impression that it may have been more popular several years ago - OCaml, Caml Light, and predecessors have been around for a rather long time, and have been used in education. It has a long, parallel history to SML.
I'm not sure about the above because I can't read French, but I remember reading it somewhere relatively 'official'. (Perhaps in the translated O'Reilly book?) Either way, having half the stuff written about your language only available in French is probably not a strong life sign.
Haskell seems to be stealing its thunder now. There are numerous "intro to Haskell" / monad tutorial / etc. articles out there, and the OCaml community seems very quiet, by comparison. I don't particularly care for Haskell* , but its designers and users have done a good job of ensuring people hear about it, and get at least a roughly accurate first impression of what makes it noteworthy.
* I don't like laziness as a default, I've been burned a couple times by portability issues (and the way that "whatever GHC does right now" has become a de-facto standard means that portability issues are probably not a priority), and it's academia-centric "avoid success at all costs" attitude doesn't sit right with me.