Personally, I dont think anything which is bootstrapped onto another companies data will ever be worth that much, unless they buy it, that is. (...summarize)

All it takes is for Twitter to implement something similar ("What are people talking about on Twitter?") and your apps life has just got harder to live, if not impossible...

I love mashups, I just don't think you should build a business on top of another service...

Yes. I have a bridge in London that you might be interested. Apparently it will be worth $9.8M in 3 yrs time.

From the auction description:

"If you believe in the YouNoodle Startup Valuation tool (not that you should), Twitturly will be worth $9,810,000 in three years. I am not sure about that number (likely not), but I am sure it will be worth far more in three years than it goes for here today."

At the very least at $10k, a months page views works out at 2c per page view. So at $10k I'd say the traffic alone is cheap, if you have a similar service that could tie into it, or a way to monetize that traffic.

Do sales like this actually happen? Is there any startup-type person out there who would/could come up with $10k to straight-up buy someone else's site?

It seems to me like a recipe for disaster and heartbreak.

I wonder how they deal with spam. Twitter doesn't even require email verification. Someone could create a bunch of twitter accounts, connect them, and shotgun URLs by script.

Doing business like this is a really good way to make money and scratch one's hacker itch: have fun bashing out a prototype, get the site going, then try and sell it a short while later.

It seems like it's more financially practical than working on open-source full time, and more fun and novel than grinding on a startup for a few years.

It would be a good acquisition for digg. For 10K, they would save a month's time and 1-2 months engineering time assuming single employee.