It really depends on what you're using Photoshop for. If you use it constantly, professionally, the update is probably worth it. Most of the changes are in terms of video and 3D use, from what I can gather. I do use Photoshop professionally, and used 7 for a long time, and only upgraded to CS when it seemed to have features I needed. It will be years before I move to a newer version, because it just doesn't add anything I need for my work.
