I would definitely get it as I do a lot of my MNing from my phone now (in bed breastfeeding dd2 - try to do that with a pc!) and the experience would be much improved by a tailored application! A cut down menu and layout to suit the smallscreen for example.
I would even pay 59p :-)
There are so many rubbish apps available - pictures of women in their bras, pretend pints of beer etc. A mumsnet one would be great!
Thank you.