Interesting thought Jeff. The time is naturally going to make this hard to implement, but from an end user standpoint it makes a lot of sense.

@Ron - think of extensions for Firefox. Some host extensions on their own sites instead of through the addons at Mozilla. As an end user I feel a little more secure installing them from Mozilla, but I'll still install directly from developer sites.

The majority will probably get plugins directly from WordPress, certainly those who would most likely benefit from having the plugin code go through some kind of validation.

Perhaps WordPress could give more guidance as to a set of standards for developing plugins and only those plugins adhering to the standards could be accepted into the repository. It doesn't solve the problem, but it could be a step in the right direction.