Thats actually what I meant. Not necessarily that job boards are the "Hot new thing", but that they are the "thing" that is easy to get rolling and always seem to attract listers.

To the people adding them, there isn't very many reasons not to add them.

So what kind of budget to companies put towards hiring? Are tech companies going to continue buying listings on every tiny job site for as much as $300+?

you'd be surprised how much companies spend to find employees. I think recruitment agencies take 10-20% of yearly salaries.

The bounty for employee referrals at the (mid-size but prominent) software company I work for is $4000 US.

If they can place these ads for 30 days on 10 of these little, influential sites, they're already ahead.