After recently upgrading from Dapper Drake to Hardy Heron I noticed that Rhythmbox was intermittently crashing (segmentation fault).
The problem appears to be a known bug.
Meanwhile there is a work-around which involves (re-)enabling the cover art plug-in. This worked for me.
Update 2008-06-06: unfortunately the problem persists. Let's hope the recent update (0.11.5) solves the problem.