Looks neat, however, I just can't see using this over something on my computer. Currently I am early in development, but my workflow is like this:
1) make tile
2) paint tile on map
3) fix tile
4) make more tiles
5) add them to the map
6) etc etc.

Later I then actually added many more tiles, and edited the tile properties to use them.

I realize this isn't everyone's workflow, but as you can see, for mine, I don't see much facilitation to that.

Also in map making, I do rapid testing against my application. I saw you had support for dropbox, webdav and iDisk. Which is nice, but still would make my workflow with this... weird.

Probably the coolest thing about this would just be simply showing off my maps while I'm on the go.

I do look forward to seeing more done though.