I've updated to GDR3 the moment I saw the article as I've had one dreamspark and 2 one dev account already in place. It is really snippy and don't see any obvious drawbacks. However, screen seems to be freaking super sensitive and even with "normal" sensitivity, OS responses are freakishly quick!
The better part I've seen is - Speech and notifications - both of them are much better than what I've felt on any previous OS. I had to always switch to USA speech pack in order for speech to recognise what I spoke, but after GDR3, it's been UK speech pack and she knows! Been writing emails and texts using voice all morning.
Notifications are not being stuck somewhere out in the woods - Kik, Facebook particular were unbearable, they've been pretty much instant-ish.
I just did not appreciate lack of true "multiple email attachments" and custom tones for apps. There don't seem to be many apps on market giving ability to set tones are text or email tones. So idea was to design something beautiful that will fill that gap. Also I wanted to give a twist to this app and let users choose to trial it - no ads, but if they feel like donate to 2 or 3 charities of their choice by paying 79p or something like that. This is just a thought, will see how market responds to this GDR3 saga.