Running kismet on my n800 was pretty impressive. Owning the first phone that could jailbreak a PS3 is a pretty good bragging point too. Watching nitdroid boot up for the first time? Awesome.
Getting my first .deb file to install (that I compiled) is pretty great too. That's when I realized we don't have to sit around crying to Nokia for updates, even if it's not 100% open source. There's still lots of things we can do to improve the devices.