empty registry keys

[jsw043]

are they a problem per say or is it just when they build up?

[Buffalo2102]

No, they aren't a problem.

Unless they build up to a very large amount, in which case you may get a very slightly longer boot-up time.  You would have to be an avid install/uninstaller of lots of programmes with poor uninstallers and not reformat/restore for a long time for it to build up to a problem level, and even then the "problem" would be barely noticable.