I have a problem with R# 4.0 which also occurs in the latest nightly builds. After a while, CtrlClick to goto declaration seems to stop working for a while. The blue underline won't show up, and when I CtrlClick, nothing happens. However, Ctrl+B or the context menu "go to declaration" still works fine, so I guess this is a problem with some mouse hook or such. Sometimes, after one or two minutes, it starts working again, sometimes it doesn't.
Perhaps this has something to do with my OS - it's Vista Sp1 64-bit.