I must have played atleast 10 hours of online gameplay this weekend
. It's really fun to go up against the best players and see everyone's different characters. I play as Youk (in honor of Kevin Youklilis in all of his greatness). It appears that the motorcycle is what all of the best players use because of it's high top end speed. I tend to like the traditional karts with the better handling but it is definitely a hindrance going up against the better players with that kart.
If you don't have it I would highly recommend picking it up. I think Koopa Cape is my favorite new level, lots of interesting terrain.