For starters Steemit != STEEM.
STEEM is a coin and a blockchain while Steemit.com is just main (or maybe we just call it FIRST) place thats lets you interact with the network and post.
Categories permanently on the left
You have them all the time handy when you want to browse, no need to visit main page all the time.
PMs Inside Website
I dont know if they are decentralized or not but people using busy.org can PM each others just within the portal.
Drafts and Bookmarks
Bookmarks is main thing im missing in Steem, when i find interesting post that i need for later i have to use 3rd party service to store it. Not anymore thanks to Busy!
Extended Profile Info
More info than on main site, esp about the voting power and also looks nicer imo.
Follow, Resteem and VOTE UP @kingscrown creator of http://fuk.io blog for 0day cryptocurrency news and tips!