Well finally: my good buddy Steven has at last done something useful since arriving at Microsoft Corp. a little over a year ago
Although Popfly itself has been getting a lot of good vibe and is certainly a cool playground for mash-ups and showcase for Silverlight, the recently announced Popfly Explorer is something that "clicks" with me a lot more. In other words: something I'll actually use 
Basically, Popfly Explorer is a tool window in Visual Studio (all editions, even Express!) that allows you to connect to a Microsoft server to upload your projects, create web sites and even host them directly on their servers, and build a community of friends where you can share code and comment on each other's stuff. So for me, the fun part is where you can directly upload your current solution to Popfly, switch to another machine, download it again and continue working. It's sort of like a Shelveset in Team Foundation Server, but then without the Team Foundation Server. And for free.
When he first described this to me, I was like "hey, cool, it's like CodePlex LightTM(R)(C) or something". And then Steven was all "yeah dude that's right". And I was like "yo wicked bro". And he was all like "yeah, it's so totally sweet". And then I tried it, and it actually worked, and everything went smooth, and I was all "w000000t"!
Anyway. Soma announced it a few days ago on TechEd EMEA, Steven posted a quick overview on Popfly Explorer (by the way, check out the cool picture of Steven as a kid on the logon screen!) and Dan Fernandez followed up with a bigger post describing how to build and publish web sites with Popfly Explorer. I encourage you to check it out, yo! Download Popfly Explorer Beta and get to the party!