No huge mistakes, but a few medium and small ones:
- letting DrawstringSweatpants.com drop. Actually I regged it in a shared account that I had with a person I was doing a minisite project with, we had a lot of names. I just assumed he'd renew it again until I could get around to the minisite (I was too busy for a long time). It dropped last summer - of course, the expiry warnings went to his email - and in the fall I'm 'Okay, let's do that one', and he's 'It's long gone'. I could have shot something. Huge exact monthly searches, stellar minisite name. It was scooped up by a dropcatch, now it's an Epik site.
- regging a bunch of terrible names early on, simply not knowing they were terrible. You know how we newbie domainers were so excited by crap names back then, thinking we'd get a million bucks from each one
- letting drop a bunch of names that actually WERE great names, but I didn't know it once the original attraction wore off. Man, if I could only go back and cherry-pick from the lists of names I let expire. I just want a dozen of them or so. Please let me take them back.
- putting off regging names I KNEW were very good, simply because I figured I'd think on them for a little longer. Like, a month or a year. Ah, inlinking.com, dateViolence.com, rollingLaptopCase.com, Fiyt.com (great fight brandable), and about 300 more names like that... sorry I put you off for so long. Au revoir.
- regging a dozen names at 1and1, another handful of names at Yahoo registrar. Newbie fool, newbie fool. Thankfully I figured out how to let them expire. Caught a couple of them with a new better registrar.
- buying a few good LLLL at the height of the LLLL spike, then selling all of them for a third or a quarter of what I paid, a year later. Ouch. But then, I don't feel as bad as some LLL owners; there was a time when you couldn't buy an LLL for less than $6500... and a lot of the 'crappier' ones are now selling in the 3000 - 4000 range.
I think that's about all. Oh, and registering a few typos and TM names back in the day. I haven't had any of those for a few years now though.
Actually, it's my domain partner that made the big ones. She paid $6K for that stupid StoresOnline fiasco, this company sent reps all over US and Canada, revving up people at seminars/talks, selling huge and vastly expensive courses. Total schlock and it took in a lot of people. She didn't tell me she had done the thing until it was over. I wasn't angry, just wish I had known; man, if she'd taken that 6K and bought up every ccc.com for sale at the time for $50 (which is what ccc.com's were going for then), we'd have made 5 - 6 times our money back by now.
- she also fell for an appraisal scam, paid out $60 before we figured out it was a scam.