Not exactly a *customer* thankyou...
Years ago, during a bit of a career stall, I ended up being a junior code monkey for a company.
One afternoon, I wandered through the Finance department - to find everyone absent except the Finance Director, who looked about as grim as could be.
It turned out that their computer system had gone down hard - no-one could do anything, so all the staff had been sent home. They'd phoned Support, who couldn't get there for 3 days, and would do a bare-metal reinstall of the whole system when they did.
Now this was a NetWare system, and I had previously supported NetWare. So I offered to take a look - after all, I really couldn't break anything, as the support guys were going to nuke everything from orbit anyway.
It took me 10 minutes to find the problem.
It took me 20 minutes to summon up the courage to apply the fix.
The following morning, I got in to work to be told that the FD was looking for me - urgently. "Crap", thinks I, "I've broken something". With trepidation, I headed for his office.
Whereupon, I was greeted with a huge beaming grin, and a very large bag of beer.
 Spookily, my NetWare support role was in exactly the same building as this fault...