Haven't tried it myself, but from what I've heard from people who have;
There's nothing significantly good about it at the moment, it merely emulates a 32-bit environment in a 64-bit environment.
It's still in its BETA stages
The vast majority of applications still run in 32-bit so there's no real advantage there either
There seems to be very little to make the switch to 64-bit OS worthwhile as it stands, while so many programs aren't made specifically or even made at all for 64-bit, so while there may well be few disadvantages there are few advantages also.