This is a good program for adding special effects to pictures. The effects themselves belong to Core Image, part of Mac OS X 10.4 Tiger. Image Tricks exposes a good number of Tiger's built-in effects. Overall, it's stable and pretty easy to use. There are a few usage quirks, which are explained in the built-in help.
Image Tricks also has some rough edges, which is to be expected with a 1.0 release. There is no "Revert" command. You can't un-apply a filter, except by choosing another filter, or reloading the original image. This gets troublesome when cropping, because the crop tool will save changes from the previous filter, whether or not you wanted that filter.
Overall it's a pretty solid program, and you certainly can't beat the price.
Tip: If you have Xcode Tools for Tiger installed, check out /Developer/Applications/Graphics Tools/Core Image Funhouse. It's a lot less stable and friendly than Image Tricks, but it has more effects, and it lets you add/remove effects more flexibly.