Question
I have two sets of steps and a platform at the entrance to my home.  I would like to tile or pave it.  There is way too much concrete to remove and start new.  Can I seal it and go right over existing concrete with just a skim coat process much like an indoor tile applicaiton is done?

Answer
Yes, if there are no big "chunks" missing or obvious cracks & failures that need reconstructing first.  Just tile over it using a thin-set mortar or whatever the tile supplier may suggest for your weather region (North Dakota versus Hawaii).  

I would avoid glazed or slick surfaced tile (like some slates or polished granites) as they are just too dangerous to have as a walk-on surface for and entryway. Think icy or wet winter weather when selecting your pavers/tiles.

-Marc