We cruised our 40' mono (Catalina 400) for a year and then lived on it for a year. We have since sold the boat and moved onto a horse farm ;-)
If I could do it again, and the cruising was similar (island hopping Bahamas or the carribean) and did not involve crossing any oceans or rounding any horns, I would definetely choose a Catamaran (assuming money is no object).
The catamaran is a much more comfortable cruising plaform once you are at anchor, even compared to a mono like our C400 (with it's large cockpit and interior volume).
One huge advantage of a catamaran is the closeness of the salon to the cockpit, it allows the galley slave to be part of social activities in the cockpit while preparing food and drinks. When the weather is inclement it is nice to be able to sit in the salon and actually see what's is going on outside.
Some of the larger cats also allow you to sail/motor from the nav station with joystick controls. Nice in bad/rainy weather.
Ease of getting in and out of dinghy is a big plus. Nice sturdy davits another. Ability to add enormous amount of solar panels to cockpit hard bimini.
Private owners states room is nice. lagoon 400 and 420 has very nice starboard hull statesrooms.
Drawbacks: galley storage and counter space can be on the small side (see Lagoon 380)
Also - the interior seems to be less woody and more plastic than most monos.
As far as performance goes, there seems to be a huge difference between a cruising cat like a Lagoon 380 and a performance cruising cat like the Aussie built Fusion 40. we sailed from the Abacos to Ft Pierce FL ( a 24 hr run) on a broad reach with wind strength varying from 10 to 20+ over 24 hrs. the Lagoon 380 started from same place as us and we were probably 500 ft behind the at FT Pierce inlet. The Fusion 40 started 1-2 hrs behind us, overtook us as we entered the gulf stream and then we never saw him again. Admittedly the Fusion guy was a very accomplished sailor and flew a cruising chute (during the night...brave...)
Andrew, take a look at the Aussie built fusion, they come in kit form and you can a professional yard finish them to your spec.
Fusion Sail Catamarans