I just picked this up yesterday. I was hesitant because there's a review on Amazon where a guy said that the WiFi play suffered because of it slowed the game down. I was hoping that this was a quirk (it happens in Mario Kart sometimes) so I figured I'd give it a shot.
I played random people yesterday and, in the afternoon, I had no trouble at all. It was nice to play someone else beside the computer.
Last night I played online and I had the slow-down issue.
Also interesting that both times that I played I was only matched up with one other person. It's like there's me and one other guy who were playing Bomberman WiFi in the whole country.
Anyway, when it works, it's great. It does suck when there's network issues, though.