ReadWriteWeb notes that, after much speculation as to how Twitter would find a business model to support its burgeoning social network, the red-hot start-up is now, finally, showing ads. This anti-climax is almost like Freddie Mercury, the lead singer of the not-so-subtly-named QUEEN, finally revealing that he was gay in 1989: Everybody saw it coming but wondered what took so long!

The flamboyant Mercury waited until AIDS had nearly finished him to admit the obvious (and, sadly, died shortly thereafter). For Twitter, though, embracing advertising is not the end but the beginning. Twitter's growing popularity has meant little to the company other than increased costs. But now advertising will let Twitter "monetize" its success, while empowering users to "vote" for Twitter without having to pay a cent for the service.

I suspect that Twitter has waited till now to start showing ads--and that venture capital investors were willing to fund Twitter during this stage--because it seemed to make sense to "build critical mass" first, before trying to monetize viewership. This has been, in principle, Facebook's strategy, too, as I've discussed.

By following in the footsteps of so many other ad-supported titans of the Internet--from Yahoo! to Google and everyone in between--Twitter may finally have started to grow up. The next step in its evolution will be allowing advertisers to target ads to users based on their Tweets, which will increase the profitability of ads on the site. After that, Twitter will face pressure to offer advertisers more sophisticated forms of targeting, such as targeting ads to users based on their browsing "behavior" (other sites they've looked at). Just imagine the outcry!