You know when you've done enough when you consider polishing with toothpaste!!! On a more serious note I find 'Tetrosyl' Rubbing Compound to be superb at polishing hulls and foils. If your local Motor Factors doesn't stock Tetrosly then maybe enquire about an alternative rubbing compound as I'm positive you wont be disappointed with the results.
For general hull cleaning I use a caravan/boat cleaner, it can get rid of light marks whilst at the same time provides a very light 'T' cut to the Gel coat. There's also very little detergent so no problems with sliding about afterwards on the gleaming hulls <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />