I've only found NetBeans useful under Windows. I've had a number of interface problems on Linux and OSX that make it unusable. (Dialogs showing up blank all the time and other problems)
I've found netbeans to be faster on windows, certainly. Not had any of the issues you mention on OSX - just general 'java is slow' issues (especially when compared to same version of nb on windows).
On Linux, I got tired of Eclipse-based Java apps not working properly - blank windows, as you mentioned being a primary issue.
I have used NetBeans both on Windows as well as on Ubuntu. I haven't noticed slowness on Ubuntu (with 4GB RAM) apart from the loading time. I have switched to VIM since then and haven't used NetBeans in the recent months though.
