Thanks to all for interesting replies.
I agree with the input that people should be able to right their own cat themselves using aids if necessary, but sometimes this doesn't work out and there is still a need to render assistance. It sounds like leaving your boat to drift freely or leaving it on a sea anchor is not an acceptable soultion just because there is too much risk your boat may end up sailing off or drifting too far for you to get back to it if there was trouble righting the distressed cat.
Our lake is relatively small, maybe a mile across, and winds are most commonly 15 mph or so with 1-2 foot waves but you can get caught in more wind unexpectedly. There are lots of docks and beach around the lake. In these conditions, leaving your boat to help another may be more appropriate than if you were in open water or in areas with breaking waves, currents, and cliffs/rocks.
The idea of lifting the mast top sounds like it could be useful if someone capsized in a gust but the conditions were otherwise tame. In rougher conditions I could see how this would be asking for trouble.
I was worried about tying the two boats together but it sounds like this can also work in non-survival conditions. If it's always the case that the upright boat will drift faster than the capsized boat, then sailing up to the disabled boat, throwing them a line, and swimming across after the upright boat is put in irons and the lines tied off as suggested in the replies may be relatively safe in non-survival conditions. I am a little reluctant to actually drop the main during this procedure since I imagine it could be tricy to raise it again with the boat rocking about in the waves - how many others do this and how hard have you found it to do? If you ended up with the sail stuck only partially up I would think you could get into some trouble of your own in the process particularly with the boom getting in the way of steering the boat and the potential for the boat to sail out of irons due to a combination of waves and the fact that the main is no longer helping to keep it in irons.
Any additional experience or input will be appreciated.
Jerry