What's cool about it? It's nearly impossible to list all the features that PeopleBrowsr offers. Besides the features already mentioned, you can search within, and post to, a number of social networking services such as Facebook and FriendFeed. You can follow somebody simply by clicking an icon in their tweet. And you can use a "Helicopter View," which lets you watch the top tweet on each of your stacks simultaneously. You can open a pop-up that shows your own stream, your profiles for the services you belong to, and what tags you can be found under. You can even find out which tweets are within a certain area (for example, I was able to find out how many tweets about "e-book readers" originated within 300 miles of London).
The emphasis here is more or less on marketing, to the point that PeopleBrowsr offers to "make your group viral" by creating a hash tag using the group name, creating a message that asks people to retweet the message in order to join that group, and then automatically adding to that group all those who do actually retweet.
What needs to be fixed? Remember when people used to make jokes about amateur publishers who had just discovered desktop publishing software? Their documents would be so full of different typefaces, colors, sizes, what have you -- you know, the typical ransom-note style -- that you didn't know where to look first. That's PeopleBrowsr. Even at its simplest -- the Lite version -- the interface is pretty busy; when you get up to the Advanced mode, the crowd of colors and icons makes it difficult to concentrate on the tweets.
PeopleBrowsr tries to make things easy for you at the outset; when you first sign in, it asks you to mark off your various social networks and then guesses what topics you might be interested in. And yes, each icon has a rollover explanation. But all the noise makes it difficult to concentrate on what you're actually working on.
Final verdict: PeopleBrowsr offers a vast number of features (as I type this, I keep finding more) for those who are serious about their Twitter use. Many of these features are interesting and can be very useful for marketing workers and others who use Twitter for professional purposes. Its only drawback is that there's so much going on that it's difficult not to be overwhelmed.
I first heard about Seesmic from a former TwitterDeck user, who said that this desktop app (still in beta) could be the Next Big Thing for people who need to track a lot of different Twitter threads.