Well, some would say Eclipse rather than Netbeans now.
I'm a total Eclipse-head these days and need it like oxygen. The context switching used to bother me but I've found having a separate "install" in a different directory keeps things clean in some cases. There's just no reason for me to have Apex/Visualforce projects in the same ever expanding project repository as Radrails. Plus things get a bit "corrupt registry-like" when you go nuts trying out various plugins.
So keeping a relatively lean and focused set of plugins for targeted areas really works nicely IMO. Initial load time is my biggest gripe with Eclipse but it's worth the wait

And Subversion in Eclipse for team development - especially for cloud computing - just kicks ass. Also though I haven't touched it yet, I hear CruiseControl blends nicely as well.
EDIT: Some plug-ins like the Force.com IDE are not compatible with the latest versions of Eclipse (yet). They all make their way to the current release on their own schedule so having multiple repositories/eclipse directories works well for me
