Well, I like the fact that I can find manufacturer's data online easily enough. And I like the sorting methods so I can look for DWG or RFA files...or SKP or PDF should I want that. Also, the 3D viewer built into Seek is pretty cool for examining the models before I decide to download. I think if it's maintained and standards are adhered to and it grows, it'll be a great service to users. Let's face it, when a builder builds a building and they're using an Andersen Door, they don't go to the mill and cut the trees, make the plate glass, extrude the aluminum, make their materials, etc, they don't "build" their own "content" from scratch...they buy a unit and put it in place. Revit should have the same ability virtually.
I also like the fact that it's fast and uniform. I don't have to google and try to find quality families made by who knows who and to what standards.
I used it the other day thinking "hmmm..wonder if Seek has any rfa louvers?"...and was suprised to see pages (640 entries) of louver familes. Sure, I could have built my own louver from scratch, spent an hour flexing it and creating different types- but with Seek, I had exactly what I needed in just a few minutes.