I agree w/r/t to the facebook apps - I don't think they have any lasting value. And I think any product that completely revolutionizes a domain doesn't need to

I agree w/r/t to the facebook apps - I don't think they have any lasting value. And I think any product that completely revolutionizes a domain doesn't need to "go viral" to succeed - ultimately the excellence or game changing experience will cause these apps to succeed, Amazon, and the iPod are two great examples. Google was a success because they created a game changing search product - it was (and still is) vastly better then anything else out there. I think however that while everyone tries to create a game changing product, the vast majority of products are really incremental improvements and in these cases going viral helps. Twitter being a great case in point - really just an iteration somewhere between IM/Email/Blogging - but went viral enough to be important, over some better platforms such as Jaiku.