Depending on how you're going to be leveling your rogue your spec for mutilate can be vastly different.
If you are soloing, i suggest using a muti spec starting out much like this spec
. (no points in Cut to the Chase due to the fact that, nobody uses slice and dice on a mob that will die in 10 seconds...)
If you are running instances heavily to level, go with Gig's spec
usually here i'd ask you to link what daggers you would be using, keeping in mind that shard will probably have your best top end damage and will be your main hand, but considering the circumstances, you'll replace your off hand right away. However, keep in mind while leveling that you'll have the opportunity to switch out a lot of weapons, and that mongoose will still currently be your best bet for a weapon enchant. Given the expensive mats list for this enchant, i'd say you may want to keep a weapon with slightly less top end/dps with the enchant, than to pick up a new one without, to enchant.
any questions/comments/critiques please post to discuss