Stability of Rails

I'm having memory issues with rails at the moment, but I can't say yet if it's our fault or the fault of rails, lighty, fcgi, etc.

Our site is very dynmic and is getting between 30k -40k hits per day and the memory uses of our fcgi processes grows very fast and we have to restart it once a day. Unfortunately, we haven't been able to duplicate this problem off of the live server so we're having a hard time tracking it down.