The next PlayStation Network downtime for routine maintenance is coming on Thursday, Sony announced today. While the PlayStation Store and Account Management will be down entirely, you'll still be able to play games online as long as you do one simple thing.
This maintenance is expected to start at 8am PT then run until 8pm PT, Sony says. If you want to do anything online with your PlayStation Thing during that time, you'll need to sign into PSN between now and the downtime. Multiplayer should work fine and dandy if you do that, but otherwise you'll be stuck for twelve hours.
Sony's launch a browser version of the PlayStation Store some time this month, so Thursday's maintenance may be in part to pave the way for that.