You get 6 SWUs each year you reach 1K. They're good for 13 months. For example, if you accumulated 100,000 elite qualifying miles (EQMs) in 2007 you'd have 6 SWUs that you can use from Jan. 1, 2008 through Jan. 31, 2009.

Note also that, as most but not everyone on FT knows, EQMs are not the same as actually flying 100,000 miles. For instance, if you fly business class you get bonus EQMs.

As for your second question, the SWUs apply to more than one segment. So if you were to fly Denver-San Francisco-Tokyo-Hong Kong on United (if that routing still exists), you'd be upgraded all the way. It would take two SWUs to upgrade round-trip. The caveats for this are that the upgrade space must be available to use the SWUs--the further ahead you buy, the better--and that you can only get the upgrades once you buy the ticket, not simply reserve it. But you can check beforehand just before purchasing to make sure it's available--I do it by phone with the reservations agent, but I think you can do it online through the UA website as well.