[x10guy]

I run all the time with it. I just use a cheap elastic armband that I got off ebay. It's designed for the iphone but it works fine with my Mogul. A little tight at first but now it fits well.

If you run outside, also check out:
rungps and mymotion. They are GPS programs that automatically track your time, distance, pace, etc. using the built-in GPS. It has automatic voice prompts so you if you have a BT headphones (Motorola one work awesome) you don't even have to look at your Mogul during your run. Both programs will speak all the data to you through the headphones.

(rungps is by far a more polished program but it's a bit pricey... while Mymotion is freeware).
Using the normal battery, I get 100+ minutes of runtime listening to music, and using the built-in GPS.