Two biggest differences would be Java interop (see http://www.cliki.net/Armed%20Bear%20Lisp) and concurrency support. ABCL appears to be a little clunkier than Clojure for calling Java.
Being a CL, ABCL places no restrictions about mutability on basic data structures and doesn't have the STM/agent functionality for concurrency built in.
Sorry, but for programming language, popularity is everything. It's a social phenomenon, it grows superlinearly with number of users.
And languages become popular and unpopular for a reason.
For common lisp, those reasons are:
It's ancient.
Parties interested in it can't agree on anything so its development is stalled.
It claims to have a huge library which is tiny by 2009 standards, and doesn't have vital things like network i/o or unicode. Yes, implementations support those proprietarely, yet noone cares, because it's not in standard libs.
It has problems with reflection, which is doubly awful for a lisp.
CLOS is interesting, but for most uses smalltalkingly simple OO would be much more desirable.
You clearly haven't used the language on real world project. In CL world, there is enough people interested to develop actively several implementations.
Also, you (as others making opinion on language from blog posts) are for some reason fixated on the idea of stuff in standard library. When it's not in standard, it doesn't exist. Wrong.
You forgot that in CL, library developer has the same freedom as CL implementer. You are welcome to roll your own continuations, embedded compiler or transaction layer in your chosen popular blub for example.
All your reasons are superficial.
The "ancient" argument is not worth commenting.
Unicode has just about every CL already implemented.
You can emulate single-dispatch of Smalltalk OO in exactly 0% of wrapper code.
And tools, I hardly miss something when tracing, profiling, code completion, live upgrades, image snapshots are either solved by standard, implementation or SLIME.
Also you forgot to write that "LISP is interpreted and slow" once again.
"Also you forgot to write that"
Okay. You want to argue with yourself not with me, to the point when you start rewriting my claims.
So, you go and argue with yourself.
We can hardly argue about CL when you know nothing about it.
Your "arguments" seemed like common set of misconceptions about CL, the "LISP is slow" is such a folklore that I thought you forgot to write it, that's all.
