expertise and hit capFollow

This site has the level 80 combat ratings. Disregard the post down below implying that all hit is based on the 17% model now (that part is wrong, the numbers at the top are right).

Hit cap is 9% for 2H, 17% for spells (or 14% with virulence) and 28% for dual-wield (or 25% with nerves of cold steel). Both of those talents are 3-pointers, with virulence 2nd tier unholy and NoCS second tier frost. They also have the added effect of 30% resistance to dispel on diseases (virulence) and 15% off-hand damage (NoCS).
If you are DW, your strikes will still have a 9% base miss chance, I believe that is lowered to 6% with NoCS.

Expertise rating converts to expertise, which each expertise gives an 0.25% reduction in your opponents' chance to dodge and parry you. Since level 73 mobs have a 5.6% chance to dodge/parry, you need 23 expertise (5.75%) to be over the cap.

Looking at a Frost DK's WWS reports (granted only one sample) you can see that auto-attack accounted for 26% DPS, melee strikes accounted for 59% of the overall DPS. (Granted, HB probably wasn't used as often as it could have been, but I'm just using these numbers for now since they will probably be close to normal at least for blood and unholy). So if you assume 25% of your damage is white damage and 60% of your damage is strikes, that leaves 15% for spells. If your spells miss, the rune gets a 1 sec CD, so it won't throw off rotations too much. I personally don't think that it's worth going past the strike hit for spell hit (it's nice, but not 100% necessary, and you'll likely get a bigger DPS boost from crit or strength). If you're dual-wielding, that means 40% of your damage is coming from auto-attack + spells, but you're still not doing enough to make the extra +hit worth it.

In order to get 23 expertise, it would take 189 expertise rating. Depending on talents (Veteran of the Third War gives 6, Blood War, Tundra Stalker, and Rage of Rivendare give 5; it is possible to have 11 as a blood DK, or 9 as a frost or unholy DK if you sub into blood through VoTW, or just 5 if you go with at least 51 points in frost or unholy). Since 8.2 expertise rating = 1 expertise, it takes that much less per expertise you get from talents. Keep in mind that 189 is rounded up from 188.6.
In order to get your melee hit to ____ you need ____ rating (which will give ____ spell hit):
6%...197...7.51%
9%...296...11.28%
25%..820...31.26%
28%..918...34.99%
In order to get your spell hit to ____ you need ____ rating (which will give ____ melee hit):
14%...368...11.22%
17%...446...13.6%

With your strikes (and 2H) hit capped, and virulence, your spells will only have a 2.72% miss chance, which really doesn't matter too much. You're not going to be CCing, so if you miss every once in a while with a spell it won't usually cause a wipe.