What I have heard regarding CUs is that they are tested and the support people at MS have confidence in them. However, they do not get the wide range of testing an SP gets from having many customers install CTPs.

So..

If you have a bug that is addressed in a CU, you should apply it to a test system, and test the heck out of it. Run through as many processes/code paths as you can think of for your system. If it seems OK, apply it on production.

However that's a big process and a lot of work, so if you can wait for an SP, I'd wait. I would not expect another SS2K8 SP until next fall at the earliest.