what is "role" for?
Roles were thought up during XHTML2 to give UA's better ideas on what the purpose of a tag was.
HTML5 is incorporating these roles and eventually every tag (or maybe just almost every tag) will have a default "role" or a possible set of roles.
However there are also ARIA landmark roles which the author would put manually as an attribute on a tag; these are pretty much for screen reader users. Landmarks generally do the job of skip links except better: users can have the major landmarks announced to them on page load, and can choose to go directly to one of those landmarks ("navigation" would be the main page navigation list, "main" would be the main content (and there is really no HTML5 equivalent here since "main" would be whatever isn't in some other role), "complimentary" for extra stuff that could sit on its own like company info stuff (not tied directly to the content in the "main" section)).
Roles are also good for turning "stupid tags" like span when used to build widgets (like a slider) into meaningful objects. So when you are building Stuff That Does Stuff on a page out of plain-jane HTML elements (which are not at this point marking up content but building stuff), since there's no <slider> tag, the role can inform users what the thingie is and what to do with it.
They are of course optional but I'm quite happy with where they are going... this is a great tool for web and web-app developers.
I'll go with <nav> this is HTML5, the future of web design.
People aren't just using idiot browsers. They are using the latest of very expensive screen reading technology as well. I suppose you're willing to pay for their upgrade though.
Personally (this means opinion follows), requiring scripting simply to make a user agent understand markup defeats the whole purpose of decive-independent markup. The whole reason HTML was invented. Why even use HTML? Build the whole thing in Flash or something. If you're going to tell people they must use your software and hardware of choice just to get access to (still mostly text) content, why not just make everyone use one OS and one browser and be done with all this cross-browser dancing game. Like it was after the first browser wars, when everyone used XP and IE6. Monoculture for the win.
The future's lookin' awesome, to borrow an overused word from Mozilla.
I am not ready for the apocalypse?
Actually, two reasons:
Every time I upgrade a browser that I actually use for more than just testing, I have to waste a bunch of my time fixing all the stuff they broke, changed, and made retarded (I still have scars from the disaster of the "awesomebar"). This is just a fact of life, but I still like to do it as few times as possible. Crawling through about:config is not exactly my idea of a good time, similar to taking the toilet apart and replacing the float mechanism on the joy scale.
So in this case, not all of my necessary add-ons worked in FF4, and by the time they did, FF4 was suddenly stopped with no further security updates or anything and 5 was out. I didn't bother looking to see which of my plugins work with 5... I'm pretty sure by they time they do, 5 will be discontinued and 6 will be out.
I donated to Chris Pederick because I think the tool I use the most is the web developer tool bar, but I also use NoScript, Firebug (both of which update pretty well), a plugin to fix the removal of the Properties option (seriously yes a plugin to add back functionality other browsers have that someone thought was a good idea to remove because "only nerds use it"!), Live HTTP Headers (ok this one I could live without but it's handier than tail -f server logs), and the JuicyStudio Accessibility Toolbar (this one takes time to update). Plus I still have JAWS 10 which still just works better with FF3 (someday, I'll upgrade to 12 or something better...).
Second reason: like 99% of all software users, I do most of my updates via an automatic updating thingie. So long as I can update my old browser I'm not really willing to just upgrade to a whole new one (because of reason #1, avoiding having to fix everything they broke).
There is FF4 on the separate windows machine here, but it is only used to check that some new bug didn't totally destroy any of my sites. Apparently IE9 broke some stuff, but I'm poor and can't afford buying a whole new operating system just to check a single browser, and apparently the company I work for doesn't care so I guess that's that.
Eventually they will stop supporting FF3x OR I will upgrade my OS and it'll just come with whatever the latest FF is and I'll just have to deal with it.
Meanwhile I do tend to have the latest or near-latest Chrome and Opera simply because the automatic update-thingie does tend to just offer whole new versions instead of doing what Mozilla is doing. But I still can't WebGL.