0) A "move feature," So comments posted in the wrong update thread (like this one was) can be easily reassigned elsewhere :)
1) First and foremost, I want to be able to see multiple streams on a page, ala tweetdeck. Tweetdeck is the number one social client for a reason. I will never default to circles until it has the same kind of approach, as it is far too hard to follow multiple communities (or swarms) one stream at a time. On a mobile, there is no choice. But that's why I do most of my (155,000) tweets from a desktop client :)
2) I want to set my stream view to make comments and status info optional and/or or much more condensed. Why do i want my stream cluttered up with verbiage associated with each update, when my attention is not on that update, and may in fact,never be? A key elegance of twitter is that I can rapidly scan a dozen updates in seconds, zeroing in on that which interests me. Circle streams assume I want even one comment, or the share metrics on every update. I just don't care about the details of something that hasn't engaged me at all, yet. I want a compact, easy to read stream of items that I can digest in seconds. If I don't see anything of interest, my eye moves one column over and I'll look there (as soon as columns are supported, which I am assuming they will be :) I would like to have 3 default views, accessible from the options menu:
1 Summary view - 2 lines only, providing just enough to give me a sense of the post.
2 Compact view - just the post, with only comment and share tallies
3 Full view - The current method, with all the images, comment threads, etc
3) Distribution lists (bundles of users) accessible with a single @alias,so I can call an item to the attention of an ad-hoc group of people, who may or may not be in other circles, on a case-by-case basis. Usually, the need is momentary, and not requiring a formal circle. eg.@my_CC_list
4) A simple API with a few basics so we developers can get into this as soon as possible :)