GPS optimization, is really necessary? Some android users are experiencing GPS problems; are applications like this really useful and safe for all devices?

http://www.appbrain.com/app/gps-optimisation/com.gps.opt

What do you recommend for a 2.2 device?
It would depend on the device. Some devices have/had some real serious issues with their GPS. The Galaxy S is one of them. It can take 10 seconds for it to get a GPS lock or it could take a minute (or even more). 

If you never have any issues with your device, then I wouldn't recommend running an application like this. If you can get a GPS lock within a few seconds or so and it is accurate, then I would say just leave it alone.