You have probably already heard about Mozilla Prism, an "XULRunner based browser that hosts web applications without the normal web browser user interface." You might have also heard about Fluid, the same idea using Webkit on OSX. There's a lot of FUD and confusion on the web about SSBs, and I'm here to tell you that it's all wrong. They are not a competitor to runtimes like AIR and they are not useless either. They are not the same as a chromeless browser window, and yes, EVERYONE should use them. Here's why:
The only thing no one has mentioned in regards to SSBs is security. Security is a huge pain with browsers; when you visit a site, all of your browser's cookies are available for that site to access. People have their information stolen all the time because they browse the web while they have their bank account, e-mail, or shopping cart open in another window or tab. The plain and simple truth is, you shouldn't be browsing the web with a bunch of windows or tabs open while you are logged in to a site which has access to your essential information, because if it can access that information, ANY OTHER SITE can too.
This is why security experts recommend that you use a separate browser to access critical online applications, or that you close out your browser completely and access a critical app on its own, so that you don't risk allowing other sites to access any of your cookies.
SSBs make the whole security issue much simpler. Something that you'll notice after moments of testing an SSB like Prism with say, Gmail, is that even though you are logged into Gmail with Prism, if you open up Firefox and browse to Gmail, you are not logged in there. Whatever cookie information is stored by an SSB, like the one I use to access Gmail, is completely confined to that SSB, and safe from any web browsing you do in your normal browser.
This is security gold. Sure, there are other benefits, such as I never have to worry about a memory-heavy webapp like Gmail crashing my entire browsing session (which has happened many, many times) and an SSB gets its own Javascript thread, meaning you won't lose performance nearly as much as when you run it in a browser with other tabs open (or when you get hit by a Flash popup, which can be incredibly CPU intensive). But those benefits pale in comparison to the security that is provided by the use of SSBs.
This is why all the FUD and confusion needs to stop. If you use webmail, or you often log into sites that use your financial information, like your bank account provider, or your credit card account, or sites like Ebay, Paypal and Amazon, then you need to set up an SSB for those. It may seem like a bit more work, but it's worth preventing the risk of losing your financial information. Plus, at the enterprise level, SSBs are even more useful; for Intranet applications that have access to sensitive information which must stay within the Intranet, it's far better to set up an SSB for every employee to use than to just trust them to maintain safe browsing practices. If I had a company of my own, I would set everyone up with SSBs. I wouldn't have it any other way.
I'm hoping someone will come up with an SSB option for Linux soon; I don't care if it's Mozilla or someone else. They're far too useful to do without. Edit: Hey, Prism is available for Windows, OSX and Linux.