Rereading that article, I had forgotten about this part:

"because synchronizing files is just not a killer application. I'm sorry. It seems like it should be. But it's not."

I read that same bit again. Kudos to Dropbox - I would have agreed with that statement if Dropbox hadn't existed

That's because Microsoft is not familiar with the single most important principle when designing consumer products ... simplicity and exclusion.

Dropbox is useful because it's in essence a simple product. Every time Microsoft designs something, it has to include everything but the kitchen sink.