Thundering1 brings up a good point in asking why I would consider upgrading if 5.5 does what I need.  The answer to that is simple, there may be aspects CS3 that I don't yet "know" that I need. :)  

I have spent some time experimenting with the CS3 features that people have mentioned in this thread and I can see the value of those features.  Originally I was only interested in being able to use new brush sets, but with each passing day I find new reasons to love CS3.