The short version:
Has your Thesis site gotten messed up after an upgrade? The problem may be as simple as some lost settings. Use Thesis Design Options to restore them to your previous or preferred choices. It won’t take long so you don’t need to panic. And don’t forget to include your Google Analytics tracking codes!
The long version:
Tonight I upgraded from Thesis 1.6 to 1.8 by following the directions at DIYthemes, and it all went swimmingly. A few hours later I noticed that one of my widgets wasn’t working right, so decided to quickly revert to 1.6 so I could check out its settings. This turned out to be a Bad Idea. Not sleeping-with-your-ex bad, but definitely unwise.
After I popped back into 1.8 I was greeted by a site with an aesthetic I can only describe as OFWHTMS*. I confirmed that my custom_functions.php and custom.css files were where they were supposed to be and the versions they were supposed to be, and then I panicked. Because if that wasn’t the problem, what the hell was?
Happily my sweetie stopped me before I deleted all my Thesis files in the hope of starting all over again. We realized that the problem was caused by a bunch of Thesis settings that had come un-set in the course of me reverting to 1.6. Luckily, I had a few windows opened to different pages in my site from before the screw-up (finally, a vindication of my 40-concurrent-browser-windows lifestyle) and used one of these as a reference (saving it as a web archive before I got started in case I accidentally navigated away from the page, which I did). All the settings needed to be restored were in Design Options under the Thesis section of the Dashboard.
By keeping the old version of the site open in one window and using Inspect Element (in Safari) to figure out my previous fonts, background widths etc. I was able to reconstruct my Thesis settings in about 15 minutes. Phew!
Update: A few days after this drama unfolded, I noticed that Google Analytics seemed to think my site traffic had all but disappeared, even though WordPress thought it was business as usual. It took a few minutes of puzzling before I realized the magic traffic drop-off happened the same night as my Thesis hiccup. Sure enough, my Google Analytics tracking code was one of the settings that got nuked. Happily, I found clear instructions on how to restore Google Analytics to my Thesis settings.
*Oh Fuck, What Happened To My Site?