Change system time, to emulate… are you sure?!
Just need to emulate how would an application work in 3 month, or after 2010, or whatever. Think twice before you just change your system time to test.
If you really need to do it, do it from within virtualization. Or…
Or you might face strange effects when you switch back to current time. Some applications depend on files last modified date. And some would check for biggest time ever, to protect them self from using trial for ever…
In our case after switching back to normal time Eclipse WTP just stopped publishing to server… guess why… 
