Just on a quick think, it would be really fun if it (ACPAN) had:

A flag indicating if the subject module was in core distro. (Which version and distro)

How many times this module version has been downloaded (marginally useful, but interesting),

some form of rating so one could know "is this a respected and tested module?" especially if I'm unfamiliar with the module's subject domain (and so I don't have to almost reinvent wheels to understand it...),

A broken out set of discussion areas for each module including:

bug reports (you know it'll happen here too),

implementation disucssion,

Documentation discussion,

Author's Announcements (subscribable? email?), etc.

grantm, ignatz, erikharrison all have good ideas about this too.

It's true that I already dig up much of this data by spelunking a variety of sources, and I know that some of what I've listed is partially fulfilled (SourceForge, PM, CPAN itself, et al). However, I often find all the searching and researching tedious and sometimes quite time-consuming. Yes, it's still Much Faster than rolling my own... :) CPAN is priceless already.

Should it be a separate site? Should it really be part of CPAN itself? I dunno. The community has certainly benefitted from the various sites supporting Perl, so maybe it's not a problem to have another.

It would be terrific if the problem (if there is one) was Fully Attacked by people smarter than me (said 'people' should be remarkably easy to find :)

±0.02