Basically every Facebook app, for one.
There's also a big niche for hobby programmers who want to make one-off online tools. The code sharing makes that even easier.
There are a lot of business people that have become programmers by building increasingly sophisticated Excel spreadsheets or Access databases. This type of "casual" programming is becoming increasingly common.
That said, I think that DabbleDB might have a more successful approach--data first, instead of code first. That approach made MS Access very successful. Casual programmers care a lot about their data, but code is just a nuisance that is tolerated to get the data to "work." People want assurance that their data is always there, even when the code is broken. In MS Access it is trivial to back up your database and view/hand-edit your data.
So do 99.9% of all users. And they're right.
Random thought: how big is the set of interesting essays you can write in 100 lines of English?
Our prediction is that there is a long-tail of web apps. We want to be kind of like the pen and paper of web apps. Maybe not great for writing a novel, but excellent for smaller works.
Client-side Javascript is the QBasic of this decade--it is the first language of a lot of (most?) self-taught programmers. It makes a lot of sense to offer these people a place to expand into server-side software.
And, Server-side Javascript is spiking in popularity and utility. I am working on a project in this space as well.
I hope I am wrong. Would be cool if you could "pull down" your app if you wanted (perhaps for a ransom fee?).
Dabble db anyone? it looks nice.