[bunderbunder]

Depends on the debugger, really. One thing the Visual Studio team's been doing lately that I appreciate is working on improving their multithreaded debugging story. Nice visualizations for keeping track of parallel call stacks and whatnot. The actual step debugger itself still leaves much to be desired - the UI doesn't give you a lot of help with keeping track of when a context switch happens, for example - but even there it's not utterly incapable.