I can tell you what I'm planning to use it for...
despite philg's pronouncements to the contrary ("there is no scalability problem"), my site reached the limit of what PG can handle on my system the very first day it was live. Unlike traditional read-intensive sites, carnageblender is a web-based game and VERY update-intensive. I'm upgrading the hardware but there's only so far that will take me on my budget. So, I need to do the majority of updates to the most heavily used structures in memory and only infrequently flush to the DB.
I looked at doing this in pure tcl and the picture is hell. tcl just does not lend itself to complex data structures; I got as far as writing a more user-friendly wrapper to ns_mutex and sketching out the data structures I'd need but the more I planned it the more of a nightmare an ns_set based caching model seemed. java will be much, much cleaner if I can get it to work. As a bonus, recent jvms seem to be faster than the tcl interpreter, so maybe I will see speed gains from re-coding the 1500 loc fight script in java. Mostly though I just want java to cache objects in a way tcl is ill-suited for, and rewrite as little as possible. I LIKE tcl. :)
