I hav'nt seen any information about this, so I've had my lvl 29 warlock and lvl 19 rogue copiedSome enchants now have level restrictions. Note: the enchant is never removed from the item to which it's applied, however, the player no longer receives its benefit until they reach the required level. Any enchants modified in this way have had their tooltips updated.
pre and post 3.1:
the rogue lost as much hp as my warlock: 600 HP. 1541 -> 941
the good news:
mongoose and 40 spellpower and all other weapon enchants are still active at lvl 29.
the bad news:
not only enchantments got nerfed
some nerfed enchantments:
libram of the... head/leg enchant: lvl 50
bc/wotlk head: lvl 70/80
100 hp chest: lvl 30 (curiously 150 hp/6 stats are still restriction free)
bc leg enchants: lvl 60 and cause soulbound (wotlk leg enchants are needing lvl 80)
zandalar/scourge shoulder: lvl 55/60
shoulder enchant of the gladiator: lvl 70 (bc/wotlk shoulder enchants: lvl 70/80)
(Heavy) Knothide Armor Kit: no requirement
(Heavy) Borean Armor Kit: lvl 70
Nat Pagle's Extreme Anglin' Boots: lvl 35 (the hat is still free of restrictions)