There are a couple other threads regarding this, but I haven't found any good answers for a specific product. I've been looking at this, but I'm not sure how well the N900 would fit.

I'm currently just placing the N900 in my Amphipod hydration belt's carrier when on long runs, but I think an armband would be less intrusive while running.

Anybody have any experience/recommendations?

i have one like that for my ipod touch, and its very very tight, even for the device its designed for, i guess the armband for iphone etc. won't fit, because n900 is quiet a lot thicker..
not sure, but let's say 95%...

How about this thing.

http://cgi.ebay.com.au/Armband-Arm-C...item51966c0569

Cheap and nasty but i am def getting one to try it out as it is better than nothing!

I bought the exact same case based on a thread here. I am MORE than happy with it and at that price, it is really hard to find fault.

I've got at least 20-30 bike and runs with that case and it is holding up well. The "band" portion could be a little bit wider to distribute the weight better but it is not uncomfortable.

I got mine for like $5 shipped, about the cost of lunch at Taco Bell and I have more than gotten my money's worth.
David