Upload & Sell: On
I've tried a variety of GPS units now.
What I've settled on is a Bluetooth adapter for your camera (whatever works - I am using a Foolography Unleashed, which is the most expensive, but has the best power saving functions IMO), along with a Qstarz BT-Q818XT. The Qstarz unit has excellent power saving features, and tremendous battery life. It rates itself at 42 hours of active time, and that's really very accurate - I measured between 39-41 in my tests. That's with constant data reception; it will go to sleep after something like 20 minutes of not using it, and will stay in hot standby for a while, so waking up only requires a couple seconds.
The nice thing about the Qstarz is that it uses a very common Nokia phone battery, which you can pick up for a few bucks apiece on eBay. This means that if you have to spend a long period of time without power, you can just swap batteries.
I carted this setup all over Tanzania, including up and down Kilimanjaro, and only ended up with 4 pictures that weren't geotagged at the end (out of 3000+). I never had to think about it - I turned the GPS receiver on in the morning, and turned it off when I was done for the day. Over an 8 day hike, all day every day, I went through 3 batteries.
I tried an Aokatec receiver that had built-in GPS (no external GPS receiver), and didn't like it - when you wake the camera up, it takes too long for the GPS signal to re-acquire. I tried an Aokatec bluetooth receiver with external GPS, and it was okay, but the Foolography has better power management and is smaller. I tried the Solmeta GPS and it worked well, but was too bulky and had a cable to snag, which is bad for hiking.
I could probably write a book on this, which I plan on doing at some point to help out others in my situation. The Foolography plus the Qstarz receiver was really excellent, and I can't recommend it enough. It runs into some money, but for me, it was worth never having to worry about it on the trail. Please ask questions if you have them, because I had a lot of trouble finding information on good geotagging, and would be happy to share my experience.