with RubyMine 2.0 and earlier, it was no problem for me, to open 2-4 projects at the same time (to work in one and to look into some code from other projects, or to answer questions from colleagues).
With the 2.5 EAP or now 3.0 beta it's not possible anymore. If I open a second project, the memory usage suddenly is at 498 MB (I have a limit on 500) and RubyMine is to slow to be usable. That even doesn't change, if I close the second project. GC runs will give some MB, but the memory usage will grow immediatly. So I have to restart the entire RubyMine.
With the EAP versions I thought, this is the normal development overhead, but now it's beta and I'm still having these problems...