I've never really understood people who are constantly buying and selling and rebuying systems but to each his own I suppose.
wait for exclusive games to accumulate, wait patiently to get one for super cheap (on craig's list, ebay, taking advantage of trade in deals at EB/GS), get games, play them fast, sell everything to hopefully profit or not lose too much, making it a cheap rental. When good exclusive games come out as sporadically as they do on the PS3 and Wii, it makes sense.