In "Songsterr: A Flash Guitar Tab Player That Might Rock, Someday" [Techcrunch] Jason Kincaid writes about Songsterr and some of it's missing (for now) features:
While the player will be a great help to many novices, it’s lacking support for a number of techniques found in more difficult songs, like slides, bends, and vibrato. There’s also no support for multiple instruments, which are found in most popular songs, and some of the tabs are incomplete (for example, the Johnny B. Goode tab omits the song’s signature intro riff). However, the company says that it will improve on these issues within the next month.
Stan Schroeder from Mashable compares Songsterr to Guitar Pro in his "Songsterr Makes Learning Guitar Tabs Easier"
Now, Guitar Pro has an online competitor called Songsterr. On the basic level, it’s the same thing, although Songsterr creators claim their engine is more sophisticated than the one in Guitar Pro. The application lacks many advanced features found in Guitar Pro, but it at least supports various tunings and playing at half at full speed, and overall it looks slick and works great. [...] Still, kudos to the developers for good execution and a good idea. It definitely made me dig up my dusty Ibanez (and realize that 5 years of not playing does things to your style)
Stan also speaks about social features that are now missing in Songsterr:
The problem with it is that, although it’s an online application, it doesn’t really offer any social features. It’s like a desktop app translated into an online app, and as such it doesn’t offer much additional value over Guitar Pro, except for the fact that it’s free
Thanks to both authors for writing about us. We've got a lot of new feedback from readers of these posts and now have a better picture of what features to add in the upcoming release. We would also like to know your opinion on the social features mentioned by Stan. Friends, recommendations, forums? What do you think is missing in Songsterr?