How to get it: This is rep reward, which means you've got to hit revered with the Alliance Vanguard, and then it's purchaseable from the quartermasters of the faction, one in Howling Fjord's Valguarde, and another in Borean Tundra's Valiance Keep. To rep up with the Vanguard, you can do quests for them (which is why we're telling you about this now), and later in the game, you should be able to either champion their tabard, or pick up rep from instance runs (possibly Utgarde Keep Heroics, but we're not quite sure about that). At any rate, do all the quests you can find in the starting area, and Revered won't be too far off. Once you've got the rep you can get the gun for 46g 61s 1c, pocket change at the level.
And yes, Horde, this weapon is Alliance only, but the Horde Expedition have a bow as a rep reward that is almost identical. So if you need a ranged weapon with a nice bit of Agility and Stamina on it, there's one rep to work towards.
Getting rid of it: You likely will within the first few raids at 80, but until then it'll give you a nice foundation to begin building up your endgame gear (plus, look how huge it is). Vendors will buy it back for 9g 32s 20c, or it'll disenchant into a dream shard.
Finally today, a request. There's a whole new continent of new stuff out there -- what kinds of things do you want to see in this space in the next few weeks? Northrend newbie items, rep items that you can start working on now (like this one), Northrend endgame items, quest rewards in between 70 and 80? We're happy to spotlight a piece of loot every week, but if you have suggestions on what we should look for (or find some cool lot that deserves a spotlight), let us know in the comments below. Thanks!