Beating our webmaster after listening to his trash talk for weeks beforehand!
Racing. Getting out there and having as much of a go as you dare/talent allows/competitive streak insists, against other people who are doing the same. I still love trail riding, but the 'no bullshit' aspect of racing really appeals ATM - if you ride well enough to overtake someone during a race, they're going to have a hard time claiming that they are just out for a ride....
Riding with the wife. Sharing a passion with someone I share my life with. Sure she's a newbie and therefore... limited in her ability, but watching her enjoy something I enjoy is pretty cool. Can't wait for the same thing with the boy.
To a lesser extent, the same goes for newbie riding mates, I guess.
Working on them. Taking something that most people see as scrap metal, and making it a rideable bike again - esp one that roosts the web-master. Preserving something. Rejecting the rampant consumerism that says that we all have to lust after the latest and greatest. Being aware that this bike you've just saved was once someone's pride and joy, even if you have no idea who they are.
Just riding... I know it sounds lame, but when you're on a dirt bike, there's no mortgage, no global warming, no dickhead boss, no leaky heater core in the car that you have to fix, no bullshit. Just you, the bike and the next bit of track.