I've had a few set-ups in my time, most ambitious being a 37 gallon setup with live rock, a few fish and some "easy" inverts like mushroom and star corals. Loved the experience but guess what - the maintenance got away from me and the tank went south after being really strong for like 3 yrs.
Like I said, I loved the experience! Learned so much about water parameters, livestock, acquired a nice library of marine biology texts, and the tank was a joy and a great conversation piece. I ended up converting the marine to fresh but hope to return to the salt hobby in the near future.
You need a good, reliable local fish store and a large budget for books!
There are funny anecdotes around about new hobbyists installing like 600 watts of metal halide lights in a new reef tank and having their power bills double, only to get a knock on the door from the DEA asking if they're growing any unusual plants in the house!