I have found nice to be one of those things that sound useful, but aren't, like "digital rights management" and
the CANSPAM act. On a single user system you could do some good, maybe. My experience with many *ix flavors is that too many things niced low and other stuff stops working, and on a busy system stuff niced high never gets run. I believe it is better to leave things at the default nice and let the system handle it, at least in a production environment. On a desktop, where you are the only one there, by all means, play with it, but don't be surprised if the system turns around and bites you on the bottom for doing so.