i've read from various sources that 2 or 3 sql queries are the most you should put in to a site with a decent amount of traffic, but how many includes are too many? thanks.
As far as I know includes don't slow down your scripts very much. It depends what's in them too, obviously the more in the the slower it will be. I usually have 2-3 on my PHP pages.
Includes are faster than SQL queries, basically every single time.
However, if you want to reduce the number of includes used, just store all your includes as functions, and use require() at the top of all files.