It will also depend on the shoes. If you have a stiff higher end MTB shoe...the difference will be less noticeable.

I started with MTB shoes and Eggbeaters and the difference for me was dramatic. My 661 MTB shoes felt like slippers compared to the Specialized Comp road shoes. As other mentioned, weight plays a part in it too. I recently picked up a pair of Specialized Pro shoes with a full carbon sole. Not only is it stiffer, its noticeably lighter.

Walking is a non issue for me. Only time I'm off the bike is walking to the restroom or getting a drink at a market.