I have a Mac at the office that I use as my sit-down computer (see Pomodoro post, two posts down) and it was running 10.6 and I wanted to try a couple of apps that required 10.7 (Lion) so I went ahead and upgraded.
The problem was that the user account I was using was tied to Active Directory and 10.7 has broken Active Directory integration for tons of people out there and I was included.
I spent a long time trying various things to get it fixed, but I ended up having to download a free tool here: http://www.beyondtrust.com/Products/PowerBroker-Identity-Services-Open-Edition/
I needed to start a fresh user profile and I have no idea if there are unforeseen downsides of using this tool, but it is working again and I’m back up and running.
Also, let me say that nothing is quite as frustrating as troubleshooting problems on unfamiliar operating systems.