Got a cheap 2.4 GHz wifi spectrum analyzer on Amazon (this one: http://www.amazon.com/Wi-spy-2-4I-Spectrum-Analyzer-USB-based/dp/B002FB611E - beware, it's officially obsolete and only has software for windows).

It's kind of fun to play with.  Most useful observation so far: it looks like my Macbook produces lovely-looking clean signals within the 20 MHz range of its channel... but my Nexus S either tries to use a 40 MHz 802.11n signal (wishful thinking, guy: you're really not that fast!) or has some seriously ugly signal generation that babbles all over the place. Perhaps that explains its terrible wifi performance and the fact that it kept crashing my friend's router last week.

Also, I took three photos with the camera and emailed them to myself.  It took a super long time for them to be sent, but the spectrum was almost entirely idle during that time.  Meanwhile, I navigated the phone over to youtube and played a video, and the spectrum was busy.  Conclusion: you weren't even trying to send that email, scumbag.

This is a fun toy.  I think I'll take it home next and see if it can diagnose my suspicious wifi dropouts at home (not just on my phone).  Rumour has it you can also see interference from microwave ovens and home portable phones.