As few as possible.
Theres no point having code in your scripts that you don't use, so you should try to avoid including things you're not making use of.
That said though, you don't want to be including too many files either, so don't be tempted to put functions in seperate files.
Generally though, whatever the case, including files and compiling code is not the slowest thing going on. Running the code is where your optimization time should be spent. Spent time reducing the amount of work your code has to do and you'll get fast code. Its as simple ( :eek: ) as that.
