@Alf: Can you please elaborate? Why do you not think it's a good idea? Yelling in caps that it's not a good idea isn't necessarily the most constructive way to say you disagree lol.

@adamjgp: I have a tank that's in all iLevel 346 gear with a couple of iLevel 359 epics and my strategy has been to cap Hit and Expertise simply because it's a hard cap that I know I can reach. Yeah yeah, I know, days of capping something for tanks went away with Wrath, forgive me if old habits die hard. However, my OCD has been satisfied with this approach and so far, I've polled every healer I've run with (heroics, no raiding on my tank yet) to see if they think I'm squishy in general and so far all of them have been quite happy with healing me. So, just wanted to let you know that I think your concerns are unwarranted as far as running heroics are concerned. My overall strategy has been:
1) Stack hit and expertise to caps (I'm over 26 expertise at the moment because I find threat gen an issue against raid geared DPS and as a pally, it's an excellent threat stat).
2) Stack as much mastery as possible.
3) Balance Dodge/Parry so neither suffers more than the other with diminishing returns.
Gemming: All my gem-sockets have stamina in them while picking up socket bonuses (so red sockets have Sta/Exp, yellow have Sta/Mastery, and blue sockets are pure Sta).

Maybe it's not the best tank gearing/gemming strategy out there, but it's straight-forward enough for me to grok pretty well and I've found that my original concerns with this strategy yielding a particularly squishy tank were completely unfounded.

Hope this info helps!