Well, since you ask...
Grading is done en masse; candidates from all the clubs in the region go along together. Usually you'll find lots of white belts, a fair number of yellow, then numbers rapidly decreasing to one lonely red belt going for brown. (Black belts have their own grading.)
Just because you're in a group, however, doesn't mean that the senseis' beady eyes won't be upon you at any given moment. The higher the grade you're going for the better you will be expected to perform throughout.
Everyone goes through the basic stances, punches, blocks and kicks, and does some punishing stretching (I was terrified I would fail because I'm incapable of grabbing my right ankle with my legs two shoulder-widths apart).
Then everyone performs the First Kata (a memorised sequence of moves), takyodo shodan <sp?>, usually going over it several times until the instructors are satisfied. The white belts going for yellow belt are judged on this kata. Afterwards they get to sit down and everyone who's left goes through the Second Kata, takyodo nidan - pretty much the same as the first with some kicks thrown in. This is the kata for yellow belts moving up to orange - me, on this occasion. Yellow belts then sit down, and so on up the katas and the belts until you're left with one very lonely person performing complicated manouevres all by himself.
The whole event takes about an hour and a half and is followed by some sparring. Just for fun. Just in case you're insufficiently exhausted. Afterwards the names of those who have passed are called and we trot up to receive a certificate and new belt.
All you really need to know is that I am now an Orange Belt of the 7th Kyu. Fear me.
Afterwards I drained a bottle of Vanilla Coke then went home and had a McDonalds Dairy Milk McFlurry, which should nicely negate any positive effects healthwise.