the 1.7 updated was apparently going to be a HUGE update including a new mode called adventure mode witch never was released...yet
well the 1.7 update consisted of:
PISTONS 
clay now generates in new worlds
TNT can no longer be set off by hand (TNT is now diffusable
)
TNT can only be detonated by redstone or fire
fences Stackable
Redstone Wire connects to repeaters
Re textured cobblestone and brick blocks
silverfish texture added to minecraft.jar not in game yet
increased spawn rate of squids
single slabs now use the bottom half of the side texture
cobweb needs to be properly broken with either sheers or a sword and yields 1 string
the bed and cake textures have been moved in the texture pack file so don't be suprised if your using an out of date texture pack and your beds look wierd
Sheers were added
sheers can be used to collect leaf blocks off trees
sheers can also be used to collect wool off a sheep (now you have to kill sheep to get wool)
Weather seems to be more common
and a bunch of new bugs that notch has been playing with about pistons (why can't he just fix it the first time : P )
using a piston to push either the top or bottom half of a door causes the other half of the door to stay, meaning you can have fully functional half doors
redstone sometimes doesn't travel the full 15 blocks it should
