A new product, SpyBike, is out on the market and it partially negates the claims I made in my previous answer. The website is hideous, but the general idea appears to be:
It sits invisibly in your head tube, under your stem cap. You wave a keyfob over it to "activate" it when you leave your bike somewhere. This way, it remains completely disabled and therefore doesn't drain the battery when not in use. When activated, it enables low-power vibration sensors (again, preventing the battery from being drained). If it detects constant vibration for more than a few seconds, it uses an embedded SIM card with 2G data plan to send you a text message notifying you, and enables a GPS tracker. GPS coordinates are sent to their tracking software over the data plan, and you can view live updates on its location from your browser.
If you're set on using GPS to track your bike, this product seems like it might be at least tolerable, if somewhat of a pain to set up initially.