I think any K20 owner that purchased within the last 6 months should hold off buying this K7, and ugrade when the next gen hits. The K7 looks like a supreme rework of the K20D, and while it has better AF speed, 720p video recording and better high-speed shooting as notable improvements, it still has a 14.6MP sensor and I don't think that unless you rely on your Pentax for your livelihood that it's going to be worth the jump. The successor to the K7 will very likely have 1080P shooting and a 20MP+ sensor in addition to all the improvements the K7 brings, and I think that's the time it will be worth current K20 owners doing the move.
However for K10 owners I would jump at the chance... the K7 looks like the start of something BIG for Pentax, and addresses many previous criticisms.
A very exciting time for us Pentaxians.