I know this is a bit premature, but as I understand it now, I am pretty excited for the gear changes coming up for the Cataclysm expansion. For the most part, itemization is going to be simplified across the board; all classes, all specs, all gear slots. It reminds me a bit more of how Diablo 2 did gear, where your core stats are key, mastery is similar to D2's +skill stat, and there is no spellpower nor armor penetration. (Edit: the minute I wrote this sentence, I looked back at old D2 weapons and armor, and apparently I remembered it somewhat wrong. There was attack rating and mana regen bonuses, but still, it seemed to more simple at the time, so I am sticking with my original feelings on this.)
As a mage I am excited to pay attention to intellect again, it just feels right. In the same breath I am crazy excited to be able to ignore spirit again, as well, spirit is just a poor excuse for more crit right now, and that's about it. Likewise, I think the mastery system will be a nice way to give us our bonuses to damage, crit, haste, etc that we always strive for without needing to place them as three or five point talents in each tree that give the illusion of having more choices than there really are. 'Oh you mean I can either get 6% more frost damage or...not have it? Well, in that case then, I spose I will have the more damage, thanks?'
Now my main point for these changes; I am guessing there will be a 4.0 patch that comes out just prior to Cataclysm itself, similar to the 3.0 patch were inscription was added prior to Wrath, that will change the item stats on what we are already wearing. This won't be an issue for the mage only stuff you have equipped, like your tier items and whatnot, but that does mean that any item you have that is technically a priest item, even if it was better than the more dps slanted item you had prior, may no longer be that little bit better after the change. All that I am getting at with this is that it might be in your best interest to throw that dps item in the bank, just to see how it compares after the new patch. You do have some time though, so don't worry too much about it yet, but probably after summer time you might want to be more cautious with dumping some things.