One important thing to remember (and something Ghostcrawler and other devs have stressed multiple times) is that almost all numbers, coefficients and bonuses are going to be changing when the expansion ships, and none of the abilities are final. This means trying to say that using certain spells or stats is a "horrible idea" because of particular issues in the current game doesn't really hold up, because your class might end up needing that stat or relying on that spell when Cataclysm hits.
Also, being as the entire stat system is getting a revamp (with a lot of the current stats going away or being repurposed completely), all of your current gear's stats will also be changing to reflect this including increased armor for cloth, leather and mail users.
There is also the fact that these previews are not the whole story. There might end up being additional talented spells for your spec or revamps of various class abilities that will change your current rotation. Some classes are getting simplified and others will be getting a little more depth.
All in all, please look at these changes with an open mind and leave any preconceived notions at the door. We still have the entire beta for them to tweak and change any of the current ideas that might be lacking or might not mesh well with your class's existing kit.
Always remember to leave constructive feedback (Note: "This sucks!", "Blizzard obviously doesn't play my class," and "Ghostcrawler promised me a pony!" are not examples constructive feedback.) and tell them what parts seem clunky, good, lackluster or just simply feel "off" of what it should be for whatever reason (and always include the reason why). If you're eloquent in your post (and sometimes even if you're not), you might be the voice that gets things changed.
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From goblins and worgens to mastery and guild changes, it's all there for your cataclysmic enjoyment.