Not that i have noticed like everyone else said everything is unlock with CP's or prestiging like you name backgrounds/emblems, face paints, extra classes, gun camo
I like this better than MW2 because imo it lesses the need to boost to complete challenges to get the unlucks and also mean you can buy what you want when you want if your the correct level instead of getting X amount of kills to get an attachment or what ever
found a little list hope this helps
4 Create a Class
5 Contracts
6 Clan Tag
8 Game Mode Challenges
10 Killstreaks, Killstreak Challenges, Playercard Emblems
13 Combat Record
15 Medal Challenges
16 Gun Emblems
19 Gun Tag
20 Elite Challenges
22 Camo
25 Custom Reticules
28 Custom Lenses
30 Final Challenges
31 Facepaint
50 Prestige Mode
Prestige 1 Prestige Leaderboard, Custom Class 6
Prestige 3 Custom Class 7
Prestige 5 Custom Class 8
Prestige 7 Custom Class 9
Prestige 9 Custom Class 10
Prestige 11 Face Tattoos
Prestige 13 Clan Tag Colors
Prestige 14 Golden Camo
Prestige 15 Prestige Playlists