Since most of you people seem to be boat noobs, let me tell you how it works.  Around 34' is the smallest you would want to live on where you can get a stand up shower that you don't have to sit on the toilet to shower on.  Then around 40-42' is the longest you would want to go due to maintenance and dock fees skyrocketing for anything higher.  Also, a catamaran can net you DOUBLE dock fees due to taking up more than one slip due to being so wide.  So instead of $500 a month or whatever, it would be $1000 a month slip fees.

Having said that, most people would probably prefer a catamaran if you got the money; around $120k for a decent one you can live on vs as low as something like $20k for monohull you can live on.  I consider the vast majority of boats to be death traps, though.  I seem to recall reading about some brand new $300k+ Beneteau where the keel just fell off, instantly sinking the boat and killing the guy.  Something like that is not going to happen in a catamaran (since it doens't have a standard keel), but will flip easier.

The only reason all these monohulls are so cheap now is like I said, most people are shifting towards catamarans, so you can get a good deal on monohulls that seem to be going out of style.  I hear cats were the original boat design that evolved in the world with these Fiji-like island native people or whatever, but monohulls were better at carrying vast amounts of cargo like gold and silver.  Cats seem to be worse for crossing an ocean, though.  Most people do it in a minimum of a 40' monohull.