Small suggestion for future versions of IDEs:
It should include all basic libraries, at the moment I noticed that there are missing (at least some) AVR library files like io.h and some others and I must find and download these files separately somewhere from internet. May be I overlooked something but searching these files from arduino installation folder I didn't found them.
Right now I'am using Arduino 1.5.6-r2 BETA Windows version of IDE.
Well, post an example of a non-working sketch or library, or we're all just guessing.
Note that the arduino IDE will normally include io.h for you in .ino sketch files, so you don't even need to #include it yourself.