I have to close the Market every time it locks up (close it close it, either through the task manager or the left menu that slides out). My experience has been that once the Market hangs (I assume because of a timeout) it just stops working all together. Almost every time I've run the update link from there, I've had to close the market and come into a fresh copy to get it to do anything (otherwise, I click the update link nothing happens). Growing pains I suppose, hopefully will get better once they work out some of the kinks.