UPDATE: Ghostcrawler and Zarhym have posted many more details on the upcoming tanking changes in the thread. Check after the jump for their posts.
In preparation for the impending launch of Cataclysm, Blizzard is currently "assessing and amending" tanking cooldowns, particularly at level 85. While druids and death knights will ultimately see some changes, Nethaera has posted some specific updates that are planned for warriors and paladins regarding block chance:
Paladins - Holy Shield will be changed to increase block value by 10% (40% total) instead of increasing block chance by 15%. Since this will cause Mastery to become more valuable, the amount of block granted by Mastery will be reduced to 2.25% block chance per point of Mastery, down from 3%.
Warriors - At level 85, the value of Shield Block decreases as block value generated by Mastery increases. To remedy this, we will convert overflow of block + avoidance that exceeds 100% into critical block chance instead. Along with that change, Shield Block will be reduced to +25% block chance (down from +100%), but this will still yield a net buff for most warriors. Also in response to this change, the amount of block and critical block provided by Mastery will be equalized. Finally, Mastery will now grant 1.5% block chance per point.
So, what do all you tanking paladins and warriors think about the upcoming changes?