I wonder whether web apps need GC... after all, you're writing stateless servers (oops, I'm on the Arc forum, well, nevermind ;P)
For a stateless server, you could just go on accumulating memory for a request from a per-handler pool, and once the request is served, you throw it all away (i.e. you re-set the pool-counter to zero.)
Why would GC be unnecessary for stateless servers? Something needs to free memory once the response is committed. Either the interpreter, the server, or your webapp. I prefer the interpreter - that's why I'm not using C.