Cloud apps are starting to be everywhere these days.
Mozilla is realeasing Bespin an online code editor based only on HTML 5 technologies (mainly Javascript).
You can play with it here or grab the code to see how it is done.

I think that this kind of software is very interesting.  I played with it a little bit and I think that it is well done and includes some very nice features (it is pretty fast, scales well etc...).

But still, from a security point of view, I remain pessimistic about the privacy issue. The files are stored and modified in the cloud.

CWE/SANS published a recent report on the most dangerous programming errors, that developers should be aware of. This report is very interesting, and worth reading.
Developers really lack knowledge about security.
In addition, I think that pointing out the most dangerous errors is a good step forward toward  informing the SE community about security issues.

About this subject, i put a comment on veracode security blog.
I argued about the methods security companies are using, which include only two diffrent solution; which are: automated tools for detecting flaws AND security expert manual code audit. Well, that will work to a certain degree but i thing that is not good enough.
I will not go further because my comment is available in their blog entry.