It takes 15.77 Expertise rating to gain 4 expertise at level 70 which will lower your target's chance to dodge or parry your attacks by 1%. Basically 3.9425 rating per point.
Boss mobs have a ~6.5% dodge chance versus your attacks. 6.5/0.24 = 26 Expertise needed to negate this completely, which equals 104 expertise rating. Also keep in mind, since ranged attacks can not be dodged by default, expertise only affects melee attacks.
To gain 1% hit, you need 15.77 hit rating, which is point for point exactly the same. The normal miss chance versus lvl 73 bosses is ~28%, which equals 441,56 hit rating without talents.
Hit chance can be improved by talents, precision gives +5% hit chance which will lower your hit cap by 78,85 Hit rating down to 362,71. In the earlier post about the new sunwell gear you'd have 394 hit rating with talents, so you'd be quite close to the cap. Keep in mind that the remaining few % can be reached quite easily by changing your gem sockets, bringing a moonkin druid with improved faery fire (3%), and eating Spicy hot talbuk (1.26%).
In effect, you can stack expertise or hit rating to the same effect point for point. However, once you are above 9% hit chance your special attacks should no longer miss. At this point expertise becomes the superior way for a rogue to ensure his attacks land on a mob. Expertise also reduces the chance your attacks would be parried, but since you should be standing behind your target dodge is really the only effect that a rogue will generally notice.
If you are combat spec, and have the 41'th talent point in Suprise Attacks then your finishing moves can no longer be dodged. In this case expertise would only affect your normal white and instant yellow attacks such as Sinister Strike, Gouge and Kick.
Talents and Items
Human rogues get a racial +5 expertise (1.25%) when using swords or maces. 19.7125 Expertise rating.
Combat rogues can get +10 expertise (2.5%). 39,425 Expertise rating.
Some items that give expertise :
* Shard of Contempt : 44 (11,16 @ L70)
* Slayer's Boots : 24 (6.09 @ L70)
* Belt of One-Hundred Deaths : 25 (6.34 @ L70)
* Shattered Sun Pendant of Resolve : 18 (4.57 @ L70)
* Brooch of Deftness : 21 (5.33 @ L70)
* Shoulderpads of the Stranger : 10 (2.54 @ L70)
* Gloves of the Searing Grip : 18 (4.57 @ L70)
* Grips of Deftness : 15 (3.8 @ L70)
* Shapeshifter's Signet : 20 (5.07 @ L70)
* Fang of Vashj : 21 (5.33 @ L70)
* Dragonscale-Encrusted Longblade : 25 (6.34 @ L70)
So, in patch 2.4 if you have the weapon expertise talent (39.425), Slayer's Boots (24), and Shard of Contempt (44) then you'd be on 107.425 Expertise rating. ~3 expertise rating over the cap.
If you were a human rogue using swords you'd need 19.7 less. Meaning for your budget you'd probably want to stick with Dragonspine Trophy or Madness of the Betrayer as a trinket instead of the Shard of Contempt. Slayer's Boots have so many extra stats, that there isn't really a viable alternative to them.
See this thread on the EJ forums for the related spreadsheet and more rogue theorycraft.