I copied the question and answer below from the Net's "Ask Your Neighbor" page. I suspect it will find a wider audience here.
By the way, this string originally appeared on the MTOA List-serve.

Any pointers, advice, warnings, based on the vast experience of the group,  about Dry Tortugas. Place to anchor, etc. We have enough supplies (and space for garbage) to survive without replenishments for some time. Would like to  visit, because it's there.
Thanks,
Raoul

All seven islands are a national park. You can anchor with ample holding and depth at the fort. Don't want anything to do with it in bad wx. Have fun
More information google US National parks. go to Florida, and click on the tortugas…there are overhead pictures of all of the islands, channels and anchorages. Along with what areas are restricted etc…
Carl Hibbard

Richard and I have been there four times and it is one of our favorite places. There is an anchorage area with very good holding. When you check in with the Park Rangers inquire about the landing pattern of the twin engine plane that brings out tourists from Key West. The fort is fabulous and very interesting. The snorkling and diving is incredible. There is a reef on the back side of Loggerhead Key, it has the light house on it, that is a great snorkling area. If memory serves it is shaped like Africa! We took soda and beer in cans so we could crush them and did not use any paper products like plates or cups. Really cuts down on the garbage situation. Also, make sure your overboard sewage discharge is closed and locked. Best park is NO BUGS!!! There is a bird sanctuary there that takes care of that. Also, commercial boats anchor there and for a six pack you can get some fresh fish or lobster (when in season). It is also a jumping off place for folks headed to Mexico, South and Central America. Met some great people on their way back. Have fun!!
Richard and Judy Klawe

Raoul,
As others have said, it is a GREAT place to visit. As in don't miss it.
I am amazed at the vast majority of visitors ( boaters) to Fla who never go there and very few on the Great Circle Cruise.
You do not need a permit to visit the Fort area. The notices for a permit that you will see apply to the out lying areas
During out stay two boat loads of Cubans made it to the island. We got some pictures of their homemade boat, 16 in a very small boat. Two groups in one nt, the weather was bad which enabled them to sneak in.  The other grp brt in by a smuggler.
Make sure that your holding tank is empty before you set out as there as there are no services at all.
CCC

Claiborne:
You might want to kick in  just go to US national parks on your computer.  Click Florida click the island of Tortuga and you have all of the information available, where, permits, fees etc.
Color pictures of the entire area, and all the buoys shown, anchorages etc.
Carl Hibbard 

There are some good anchorages a few hundred yards ESE of the fort with easy access to the docks and land. Be alert for the Barracudas that hang out near the anchorages.
John Harris