I tried running 4.0 EA3 on my Windows 7 64-bit PC with the 64-bit JDK. I then immediately got a warning about my roaming profile exceeding the maximum space allocated. We have 60 MB allocated and I was using 30 MB or less prior to running EA3.
It appears the culprits are the files in %APPDATA%\SQL Developer\system4.0.0.13.30\system_cache\var\cache, specifically the all-resources.dat file which was just over 30 MB in size. I can delete this file, but it of course is re-created when SQL Developer is run again. Since these are cache files, should they perhaps be stored somewhere in %LOCALAPPDATA% instead?
I had not tried the previous EA releases, so I do not know if this is specific to EA3 or not. I have not had this problem with releases prior to 4.0, though. Our developers will not be able to use 4.0 in our environment if it blows their roaming profile space allocation.