I'm still not sure if the Twitter stream is the right place to be for advertising, but with the way the company set out to make it easy for developers to build upon their platform with open APIs, it's no wonder so many ad networks have sprung up since it got started. Its massive growth and the fact that the San Francisco startup is a media and celebrity darling probably helped in that regard, too.One of the companies that is dabbling with advertising on Twitter - even if Biz & co seem to be reluctant to do some serious testing of their own - is Ad.ly, an LA-based startup that launched about a month ago.