View updates on a subset of my accounts (instead of just one or all)

So, the updates stream shows me updates from everyone who any of my several Twitter accounts follow. If I click the icon of a particular one of my accounts, the update stream will just show those that that account follows.

It would be great to be able to select two or more of my Twitter accounts, to view the combined stream of them, instead of just one at a time, or all.

Imagine you have 3 low-traffic accounts, sharing a similar "topic" or set of interests - let's say cycling. And one high-traffic account, with a different set of interests - cats and cupcakes. To monitor the activity of the cycling people, you'd have to watch each of the 3 accounts individually, or watch all accounts at once, introducing a bunch of crazy cat & cupcake lovers into your cycling stream. Short of opening new CoTweet accounts to manage different sets of Twitter accounts, I'd be cool if you could filter the streams more closely. (A groups functionality - which I'm sure someone must be talking about already - might address this to some extent...)