I don't know if its lack of patience, or curiosity, but I start tasting after 4 days. My first 3 batches were coopers kits, and I started drinking them after a week. I'd waited 6 weeks, and to me, the beer tasted the same. Since I moved to PM's and extract with steeping, I've conditioned longer. I taste at one week intervals, if I have other beer on hand. If not, I drink away after about 2 weeks. I made a 9 percent quad about 5 months ago, and haven't tasted one in two months, and I made an 11 percent cider at the same time and haven't tasted one in just as long. I made a 1.060 pale ale that conditioned for 2 weeks, and to me, it was ready, so I drank it. I made a newcastle clone that's been conditioning for 10 days, and I tasted one and to me, I'd drink it now.
I think it depends on your fermentation periods, also. If you only wait till gravity is steady, you should condition it a little longer, like 4 to 6, or even 8 weeks. Of course gravity is something you have to consider. You wouldn't condition a 1.040 as long as you would a 1.100 barleywine, but then again, the 1.100 wouldn't carb in a week. So if you leave something in fermentation (primo and secondary)for 6 weeks, you could probably bottle condition for 2 weeks and start wacking it. But if you ferment something for 2 weeks, you should probably condition it for 4 to 6 weeks for it to be ready. I've been making 1.060 beers and ciders lately, so I primary for 4 weeks, bottle condition for 2 and start drinking. I'm planning on making a belgian strong, or a chimay white clone in the near future that I'll leave alone for half a year before I taste it. In the meantime I'll be sure to brew plenty of moderate gravity beers to have something to prevent me from dipping into the longer conditioning bottles.