You might get better responses if you post this separately on the UA and DL forums. Community is used generally for get togethers.
Having said that, the benefits, at least with UA (who I fly with), start kicking in when you fly at least 25,000 miles a year, where you get a 25% bonus on miles. The serious benefits start kicking in at 50,000 miles, when you get double miles for everything. If you're looking at mileage runs, you have a wealth of options, both domestic and international, because you can pick the best fares from among OAK, SJC, or SFO.
When you post on UA, you'll find some members like to qualify by segments versus miles. That can be explained in a little more detail over there. I'm sure you wil get good advice over on the DL board, too.
Welcome to FlyerTalk. Magic111 who posts on the NW forum lives there, too, and I'm just a couple miles to the east.
[This message has been edited by tom911 (edited 02-19-2002).]