I've never even heard of it. I checked it out and it looks interesting, but it's limited. You can't read the forums or search for patterns. It's mainly for managing your own pages. Bottom line for me...no, I won't be getting it at least at this point.
I use Yarma for Rav. I love it because I can take a pic of a knit then post it directly to the correct project on my project page. Just one step which is making me post pictures much faster. It's limited to being able to put pics on Rav and/or Flickr. That was the hardest part of using mobile devices so I was glad to pay the 99 cents.
I also need to say I do this all on my iPad, not iPhone. It's an older phone and much too slow, but I have Yarma there to use in a pinch.