Scubamarine,
My advice and tips would be that you're in for one awesome trip!
The boat ride from San Diego is long, 22 hours, and quite a few people did get sea sick. A few got sick on the first trip on the way to the island, and the second trip on the way back. So if this is you, be sure to bring something to remedy this..don't let the long ride discourage you though! It is a bit shorter out of Ensenada though.
If you are going on the Searcher (which I was on for my 2 trips) and you're tall, let them know and they'll put you in a certain cabin with a longer bunk. The Searcher is a long-range fishing boat, so if you're into luxury go on the Solmar V. I very much liked the atmosphere of the boat, and thought being on a tuna boat for a Great White trip only added to the ambience. Others may disagree. But honestly, I only slept in my bunk and never spent much time in their at all. I believe Great White Adventures are the only operators that offers cage dives at night too. That's a wild experience. I don't know if they still do it, but we were able to use the boom to tie hang baits to and see the sharks munching on the bait half way out of the water.
That was fantastic. Some of my friends that went this year said they did not do this.
GWA also has a submersible cage that I believe the other operators do not have either ??? Check out their website for pics. Very cool...
As far as equipment, you'll only need exposure protection. wet (dry) suit, mask, boots, and gloves if you wish. Many people use dry suits, but I was in a 7mm wet suit and didn't got cold. I think the water is around 68 degrees. When there were 5 Great Whites circling the cages for 2 hours I never got cold. It was only on the first trip when on day 2 when there were no sharks for awhile that I got cold. So if you only have a wet suit, like me, you'll be fine.
The best thing about it, I think, is seeing world class divers with all the experience in the world exiting the cages and saying that this is one of the coolest things they've ever done. Coming face to face with a Great White is an experience that's hard to top in my opinion! And it's the easiest "dive" you'll ever do.
I know that there are several operators out there now. I was lucky because on both my trips, 2002 & 2004, we were the only shark boat out there. In 2002 the only people going to Guadalupe were San Diego Shark Diving & GWA. In 2004 I went Aug 30 to Sept 3. Again we were the only boat out there because of the early date. If I were going to book myself for 2007 I would book on one of the early dates in mid to late August. We had MNAY sharks in August in 2004. I believe the early dates with Great White Adventures are all on the Solmar V, which I haven't been on though, but some of my friends have and said it was great boat.
I'm not sure what else to add, if you have any specific questions, maybe I can answer more for you, but feel free to call the guys at GWA they are all VERY cool and I strongly recommend going with them. If you decide to go with Great White Adventures, tell them Bill from Chicago sent you....
Good luuck and happy sharkin'
Bill Fisher