You have reached level 21!
Your shoulders have gained 1 point of armor,
1 point of agility,
1 point of stamina,
1 point of attack power,
and 1 point of resilience!
That isn't actually what happens, but it was interesting to take a look at my shiny new [Exceptional Stormshroud Shoulders] when my rogue gained her first level wearing them. My very first heirloom item does not disappoint (poor Cheery had been wearing [Brocade Shoulderpads] for lack of anything else). It's nice to know that I've going to have a level appropriate pair of shoulders from now possibly all the way through level 80. It's too bad gear can't always level with you, but I guess they need some form of non-level advancement in the game for max level.
The only real catch to them is that they have to go unenchanted because there aren't (to my knowledge anyway) unbound shoulder enchants that work on ilvl 1 items. On a character like my rogue, who doesn't have rep with the Aldor/Scryers at the moment, that's not a huge deal. For a character like, say, my Pally, losing out on the exalted shoulder enchants in level 70+ content is a substantial hit in stats. Then again, there is no other source of experience boost in the game at the moment, so weigh that accordingly.
Speaking of experience...
The 10% kill bonus stacks with the rested exp bonus. The upshot? As a freshly dinged level 21, I was a mere 59 kills away from level 22. It's been so long since I leveled a character in this region that I don't know exactly how that compares to the old school rate of experience, but I'm guessing it's pretty darned fast. I suspect that I'll be paying Cheery a visit once a week to burn off her rested exp state, and probably be picking up a level each time I do so. Not a bad deal, though I'd still argue that the bar is too high for non-DK alts compared to instant level 55 DK's complete with epic ground mount and gear.