25 to 65 MB RSIZE is normal for Adium, depending on your usage.
Remember to add the "iChat Agent" RAM usage to the "iChat" usage when considering iChat's RAM footprint. Generally, iChat and Adium use roughly equivalent amounts of RAM, with the caveat below
The WebKit framework which ships with OS X 10.4.9 (on Intel at least, and probably on PPC), used by Safari and by Adium among other applications has a major memory leak. We haven't done tests with Safari 3.0 beta yet, but the problem is most likely fixed since the leaking objects' classes don't even exist in the current developer version of the WebKit frameworks.