I hit multiples, with new niches being looked at all the time. Anything that works I go vertical on; anything that makes anywhere near break even on money and gets recordable traffic I'm likely to keep forever -- one never knows when a given topic will get hot, and as is with dozens of niches covered I've got a ready-made site with indexed pages and established traffic onto which I can graft a new promotion, maybe salvage the thing and make some money off of it after all.
Frank
Frank