Just finished buying Joikuspot, downloaded and ran it just to test on my MacBook Pro - ran great (though I'm on AT&T's 2.5G EDGE network). N900 did get rather warm as has been reported, and after reading this thread I loaded up MicroB to see if WiFi was working.

Nope. No site would load.

So I turned the N900 off, turned it back on, and it's working fine. Maybe there's something in the WiFi driver in how ad-hoc mode is being released that it's not reloading the infrastructure mode properly? Regardless, I'm ecstatic that there's at least an easy way to tether my laptop - now it's the kinks like these that have to get worked out.