"...the type of articles they wanted read. This 'set the tone' for the site as whole."
The first few hundred users of your site will determine what kind of users the site will attract, so "being" many of the first few hundred users yourself makes perfect sense, if you want to be guiding your project and not just "hoping for the best".
One of the unusual experiences I had growing up in LA was a high school club fundraiser where we all went to a sitcom. Yes, we were hired as a studio audience for an evening.
This was clever because they gave us a reason, not just an individual reason but a collective reason, to be there. We felt more engaged with the experience, even when it dragged into the late evening. We actually ended up laughing, at jokes that were not that funny when they ended up on TV.
Ultimately, what they did to get us there enhanced the enjoyment of the later users... I mean viewers. I wouldn't hesitate to get early users the same way, for the same reason.
Getting people to sit in a seat in a studio and laugh for an evening is basically a solved problem. But getting a sharper-than-average, engaged group of early app or site users is still tough. And it's desperately needed.
As others mention, Mechanical Turk is a pretty bad fit. You're probably better off getting a few friends to be sockpuppets (be sure to pick less silly names than "Nutshapio" though). Maybe a startup founder could try taking inspiration from this story to turn their public beta into a fundraiser. Oh, and I can't miss this opportunity to mention the BetaArmy subreddit:
That's about it as far as resources I've run across for getting a great first hundred users. So what are the best ways everyone else has found (apart from being in YC)? Does anyone run a service to satisfy this need?
If you are looking at the default front-page, then that can often seem the case.
But if you create an account (no personal details needed, just a username and password and there is no "no fake names" rule so there is no personal information needed) you can change the default selection of sub-groups and you end up with a rather useful (if still somewhat random) aggregator of interesting stuff. Those things you liked from the first few months are still there and if you select just those sub-reddits you care about. Some of the other stuff will still leak in, but not overly so.
Reddit is very large: there are almost certainly subreddits for that sort of stuff. As an example, /r/Haskell[1] is fairly technical (it is frequented by people such as dons[2] and gwern[3], and presumably they would've moved on from r/haskell if it became overly banal).
(Also, a brief googling turns up /r/startups[4], but I've got no idea of its standard of discourse.)
"...the type of articles they wanted read. This 'set the tone' for the site as whole."
The first few hundred users of your site will determine what kind of users the site will attract, so "being" many of the first few hundred users yourself makes perfect sense, if you want to be guiding your project and not just "hoping for the best".