A Map placed inside an Item Frame renders its image significantly slower than it would while being held by a player, upwards to 16 times slower.
Normally a Map would take around 5-7 seconds to render its image in hand.
In the Item Frame, the Map took upwards of about 80 seconds to fully render its image.
Issue is SMP only. SSP Maps in Item Frames render at same speed as being held (Not tested in creative)

Steps to Reproduce:
1) Create a Map (must have some image to render)
2) Place the said Map inside an Item Frame
3) Log out then Log back in