I'm going to lobby here for a button icon change. After several days of using a version of Flock with the round Dippin' Dots-like buttons removed, I've more or less gotten used to the photo and news buttons, but I think I've done so more out of habit and use than because they're useful buttons. There are several problems with them.
First, the photo button is too generic to accurately depict what it means. I suppose I could figure out as a new user that the button looked like a picture of some sort, but it also looks rather book-like. I could think it was a print button (as it looks rather like a printed page). I could even reasonably think it was a button that would take me to sites for shopping for art (not likely, but plausible) or to a more general image search than what we actually build in, or I could think it would perform some sort of desktop action. It's just problematic. I think going back to a camera image makes sense. It follows the model of print icons, attachment icons, and even folder icons, all of which depict an object that facilitates the given action rather than the object upon which an action is taken. One might conclude that a camera button could make people think they were going to visit camera shopping sites (again, not likely, but plausible). It's also possible that people might think a camera icon signifies interaction with the camera itself (ie, that the browser includes dialogs that walk you through the actual image download process), and perhaps that's what drove the icon change in the first place. I nevertheless think it's better to stick with a camera, as I believe people are more likely to click an icon whose picture they can clearly identify than one they can't, even if they know what neither does.
Second, the news button doesn't really look like a newspaper, and as has been pointed out sometime fairly recently (maybe in a blog comment somewhere), the old newspaper model maybe isn't what we should shoot for anyway. In any case, it's not clear what the icon means. I read a comment in irc in which a long-time user of Flock saw the icon and was thrilled at the prospect that we had integrated some sort of iPod interactivity into the browser. I tend to think it looks sort of like a calculator. I'm ok with the non-candy buttons we've got now, but I think that if we stick with the newspaper icon, something closer to what we had on the old button does a better job conveying the idea (my wife proposes that making the photo live in only one column might help). I can't really think of an alternative icon that would convey what the button leads to, unless we go with the standard RSS icon that appears in the urlbar. This would be problematic because that icon probably doesn't mean much to most people (neither does ours, I argue), but at least there would be consistency, and people would be better equipped to conclude that there's a link between the toolbar button and the urlbar icon. So consistency between the two ui areas might make sense, in any case.
Third, the photo button and the news button look enough alike that it's hard to distinguish between them visually. Thus I find that I distinguish between them based on position rather than on depiction. This seems like poor usability to me. Even if we continue to use vague, unidentifiable icons, I hope we provide broader differentiation between these two. One user has commented that he thought they signified a landscape/portrait distinction, and it occurs to me that they look enough alike that one might think the photo button shows only a preview or only images on a page, while the news button shows the full text or adds captions or annotations to photos. They look, in other words, as if they signify slightly different views of the same information rather than two utterly distinct browsing functions.
Fourth, I don't think the "lit" states of the buttons are bright enough, and having them be different colors for the different buttons seems bad. It's like reducing the brightness of traffic lights and letting different cities or even different intersections define which colors (and positions) signify which signals. When looking at the old buttons, I didn't even have to try to notice when my photos or news were updated because the bright complementary orange jumped out at me. I now have to do some cognitive processing to determine whether or not the buttons are lit up. Standardizing the color of the lit states would cut some of this processing, as would making them brighter. I now find myself back in the position of having to think to check for updates to my photos or news. Admittedly, the check is easier than it was before we had buttons that lit up (I visually scan the buttons, look for subtle green or purple shading, and behave if/as needed rather than having to click a button to go to my bloglines account or click a few things to look around in the photo topbar), but it's harder now than it was in builds from a week ago. My vote is for bringing back bright orange states that alert me to changes.
I say all this, of course, as a user and not as a certified usability guru, so take it for what it's worth.