Up-Down was crazy busy when I went there. I couldn't actually play the games. 
Yeah, it's crucial to avoid peak hours (about 7-11pm). Especially avoid Fridays and Saturdays. Early in the week is prime, and you can pretty much have at any game you want for hours.
Yeah, but where's the thrill, if nobody's watching you over your shoulder while you're being awesome?
Thought I'd also share this experience from a couple months back:
We've got a couple barcades around the San Diego area. The Coin-Op Game Room is one I had been to a handful of times, for Sunday Street Fighter 2 Hyper Fighting tournaments. It was never too busy. Maybe 30 people max, including the 5-15 people there for the SF tourney. The tournaments stopped happening after a couple months, and I hadn't been back in probably a year to a year and a half.
Then, my gaming partner and I decided to go check it out as part of one of our marathon "gamin' Saturdays" that we try to get together for every other month or so. Start as early as possible (10-11 a.m.), drink beers and play until we can't play no mo' (usually around 10-11 p.m.).
We checked out their current web page and saw some pics showing a Donkey Kong on-site, which wasn't their the last time we had been there for an SF tourney. So, we committed and went.
Sadly, there was no DK...it must've come and gone during our hiatus. But, the place got packed. We got there around noon. There was the usual 20-30 people when we got there. By 3 p.m., there was probably 100 people in the place. It was that great old arcade feel, lots of people vying for the games, continuous competition on SF2 (well, that's something I like, at least)...and now with beers.
Would've been better with a DK, but to the original point, the scene is doing well...at least at the moment.
