multiple directories

When I've upgrade my arduino compiler I never gave it much thought. I look now and see that I have and arduino-0022, arduino-0018 and arduino subdirectories, each with their own library directories. Is this a problem? Do I need to delete these older version?

You can safely keep the old versions if you want to. The library folders under each version are the standard libraries used by that version. Any user contributed libraries should be in the libraries folder in the folder where you save your programs, so will be accessible to all versions of the IDE.

What version of the IDE are you currently using ?