Not for long though, 4.2 is just around the corner. I can't see them doing too many extra betas before releasing it.
By the time you develop your app with this library 4.2 is probably going to be released anyway.
Still, its not like I'm doing more work anyway, going with ARC saved time on development. If Apple ends up never releasing 4.2, I would just had to "finish" the job.