Finally took a look at ArcGIS Online, released in May this year. I now feel a wee bit like Mike Doonesbury circa 2000:
So I've been working for a few months on an open-source workflow that runs between a web map and an editable database with embedding capability, actually pretty psyched that ESRI wasn't in that space yet. I wish I'd tried this out months ago:
View Larger Map
It looks like you still need some ArcSDE and ArcGIS for server chops to pull off a completely-editable interface - to actually practice vector editing in a webpage window - but this was frightening. I threw the above map together in 30 minutes using ArcGIS Online, while coding something similar from scratch took closer to 40 hours (though I'm no programmer).
ESRI strikes again.