This an old thread, so maybe I'm too late, but I'll add my $.02 anyway.
I have made my living doing underwater hull cleaning for 11 years, so the advice I impart here is born of much experience. Unless your hull is very foul or the paint is in poor condition, you will find that Scotchbrite "Doodlebug" pads will do a very good job cleaning. The blue pads will work in most situations. Brown for those hulls that have not been cleaned in a while, white for new paint or bottoms that are cleaned very frequently. If you need to use a black pad, you may as well use a metal scraper. It won't harm the paint any more.
For the running gear, I like to use a Rubbermaid wire brush that has a small scraper on the end. This makes short work of any plant or animal growth on the prop, shaft, strut etc.
You will find that a small suction cup device is almost indespensable for keeping yourself close to the work and giving you some leverage to apply elbow grease when needed. Although I make my own out of the business end of a small plunger and some 3/4" PVC pipe, West Marine (and maybe our hosts, as well) sell a suction cup designed for this use. I wouldn't try to clean a hull without one.
The last tips I would pass on are health/safety related. First, never clean a hull without wearing a hood of some sort, even in warm water. You will be knocking a lot of crud and bugs off of your hull, none of which you want to end up in your ears. Second, never dive a boat that is plugged into the shore power system. Electrocution can ruin your day.