I'm not a great hill climber by any means, but I, too, do a mix of standing and sitting. I read somewhere that if you stand and you're not super close to the top, that you should keep it to 8 to 10 seconds, then sit and spin, then do it again. I think this has to do with the amount of time it takes for your muscles to recognize lactate buildup or something (12 seconds?) so you're working at your LT but not for long enough to burn out immediately. I count pedal strokes (sometimes half pedal strokes, a number as each foot hits bottom of the stroke)

You know, I have to ask about all the people who say they just "spin up the hill". I get the theory. But there are plenty of hills where I'm in my biggest, lowest gear, and I'm still pushing barely 50 or 60 rpm and "spinning" as a perceive it is simply not even an option. There's one hard hill near my house that I ride pretty regularly - it's oly 140 feet of climb over just under a quarter mile. It feels brutally steep, but I think it works out to only being about 10.6% grade. And there are people around here talking about 26% grade?!?!