Acquired in October 2007, Twitter rival Jaiku still doesn't accept new users. Its current ones complain of system slowdowns and malfunctions. On May 30, 2008, founder Jyri Engeström wrote:

Contrary to some voices out there, we DO have plans for future development and we will involve our developer community as much as we can. Just to reiterate, we are working very hard to ensure you have a useful and usable service. We feel the short term pain, too.

Acquired in October 2006, JotSpot is Google Sites now, and according to longtime users, it's not what it used to be.

Purchased in 2005, it took Google six months to assign any new engineers to the project. The founders quit in 2007, and one, Dennis Crowley, will tell any entreprenuer who will listen to reject Google's siren song.

Google acquired GrandCentral, which provides a suite of telephony services, in July 2007, immediately closed it to new users and hasn't opened it since.

Google acquired Measure Map in 2006, hoping to incorporate its features into Google Analytics. "And we did that," reports Google VP David Lawee. Too bad for bloggers who missed Measure Map's blog-specific features and don't use Google's Blogger.

Joi Ito, an early Twitter user and an investor who helped launch the service's Japanese version, said in April that the wireless theory doesn't apply. Early on, Japanese users were 30 percent of the service's base, a percentage that has fallen as it has grown in the U.S. and elsewhere. But they used the site despite its flaws. Though Japan has long been text-message crazy, Twitter didn't have a Japanese SMS service at first. Even entering a message in Japanese characters required a workaround.

Ito thinks that Twitter's simplicity struck an emotional chord in the famously minimalist country:

It got crazy early adoption in Japan from the beginning. One of my theories is that a lot of services in Japan to be either closed or over-featured portals and simple services with good open APIs are not as common as in the US and it attracts developers and users who are sort of sick of a lot of the bloaty Japanese services.

Here's another theory on why Twitter spread: Ito himself. Though he's too modest to say it, the globetrotting venture capitalist is a key bridge between San Francisco and Tokyo. Could it be that Twitter spread in Japan in part because Ito, Web 2.0's trans-Pacific import-export specialist, took note of it, and others followed the trendspotter? We are talking about a social network, after all. People may stay because of their features, but they join because of their friends.

As late as last year, Ito was hedging his bets, favoring Twitter rival Jaiku in April 2007: "I've been helping the Jaiku guys out a bit as an advisor and I'm also a friend of Ev's." (That's Ev Williams, Twitter's founder.) Less than a year later, Jaiku had been sold to Google, and Ito announced he was investing in Twitter. It's not an explanation that coders will like, but Twitter's spread in Japan suggests success really does come down to who you know.

(Chart by Pingdom)

What this tells us: Jaiku, which has a much smaller and more European user base than Twitter, isn't really doing it for Google. Could Twitter founder Evan Williams, who already sold his first startup, Blogger, to Google, get a second payday? That would be one way to solve Twitter's problem with finding a way to make money.