I'd just like to add that I am a WP7 user too, having bought the app a few days ago (for £8 or $12.67) before visiting the forums.
Baloo, your infomation is incorrect. WP7 users do not recieve premium caches if they are not premium members.
As I have noted within the first few days of use the app is buggy, which is annoying. GS oviously thought it worthwile to release the original app to people. I don't fully undersand the situation and did not recieve an e-mail, possibly because I bought the app after they were sent.
However, it seems that WP7 users will have to pay for another, new app which has decreased functionality over the original. If you want the normal functionality of the old app, you are required to be a premium member, a side effect of which will be being able to see premium caches.
Geocaching is a casual thing for me, hence I do not want to be a premium member and conviction to the hobby is low, therefor I am not willing to spend much on it. I am also a student with a limited buget (to the guy who said how can you afford a smartphone....a phone is pretty much essential these days and I pay £10.99 or $17 a month for 24 months for my phone and service.)
Also I expect an app to function without buggs and be patched a reasonable intervals and be usable for the entire device's life. You patch an app, not remove it and expect everyone to buy it again after for reduced functionality.
I'd also like to add that paying for an app when it is buggy, makes it not fit for purpose.