I have shamelessly ripped-off today's post from my co-author, but the topic just spoke to me so I stole it. Index tuning is not particularly "sexy" among the jobs that fall under "what developers do" -- it's a bit tedious to track down a poorly written query or have a table reach that magical rowcount that sends your response times into a tailspin. And while most of my experience with index tuning has been carried out under duress I find it a satisfying task nonetheless. There is something about seeing a minutes/hours long query become seconds/milliseconds almost instantaneously upon application of the right index that just makes me smile.
Title: How often is that entered as a lesson learned? Snarky: Our PM asked me to look at the lessons learned database. It's grown large enough that it needs its indexes adjusted.