We've posted this on the Force.com IDE pages on developer.force.com before, but I wanted to remind everyone on the boards that the Force.com IDE is compatible with Eclipse 3.3.x and 3.2.2 only.

We have not tested the IDE with Eclipse 3.4, and while this is on our roadmap we do not know if or when it will actually be blessed.

Today we learned from Steve Andersen at gokubi.com and Scott Hemmeter of Arrowpointe that in Eclipse 3.4, deleting a Force.com Project from the Package Explorer may risk deleting the metadata components in your project from the server as well.  We have confirmed this behavior does NOT affect Eclipse 3.3.x or 3.2.2.

Until salesforce.com announces Force.com IDE compatibility with Eclipse 3.4, we strongly recommend sticking to Eclipse 3.3.

Jon