I don't have a personal experience using a SteriPEN but I did meet a couple that had the light(?) burn out on them at Glenns Lake Head. They had to borrow a filter from others or boil water.
I bought the Steripen Adventurer in the Spring and have been using it for about 8 week-end trips during my Glacier training season in the hills of Allegheny National Forest.
The first thing that I had to do was replace my water bottles which had an opening too small to get the pen into. After I invested $20 in two new water bottles, everything has been great, I've probably used it 10-12 times so far on the original set of batteries and no problems.
The real advantage to the pen is that for a liter it takes only about a minute to purify the water and it claims to get rid of all the varieties of nasties, plus it doesn't alter the taste.
I've had mine for 2 seasons now. I still love it. It takes a bit of getting used to as far as making sure the electrodes stay in the water so the light stays on the whole time without giving you the red light error. I just make sure the bottle is always full. I'm still on the same set of batteries after about 50 liters. So far no complaints.