Ok, so that title is a lie. I really couldn't care less what the actual program itself brings to the table because as an end user it will never affect me.
First of all, I love Firefox. It's much easier to use and offers greater extensibility than IE. The Firefox 3 beta 5 uses less memory and renders much quicker than most competing browsers. However, although I may not benefit directly from the release of IE 8 (because I'm a Linux user), as a Firefox user, I still stand a lot to gain by Redmond's release. I do quite a bit of web development. Dealing with the headache of trying to make pages render correctly in older versions of IE and standards compliant browsers is enough to make oneself consider a change in profession.
Honestly, I don't know enough of the idiosyncrasies between how the browsers render CSS, but I do know enough about their Javascript differences. And while it's possible to do almost everything in old IE that you want to do in a standards compliant browser, it affectively means your code doubles because you end up writing another copy of your code that uses ActiveX specific functions. Also some versions of IE don't garbage collect correctly when a variable goes out of scope, so you have to write extra code to handle those cases as well.
Microsoft's new push for standards compliance as well as trying to set the next standard is admirable. Since this is Microsoft we're talking about, the IE8 beta still shows some minor non-standard behavior (at least from the screenshots I've seen) however with a standards compliant web page, it will render similarly enough to other browsers that it won't make me rewrite all my code. (this happened to me recently when I forgot to check this page in IE; most standards compliant browsers support SHORTTAG despite SHORTTAG not being in the XHTML standards)
So this brings me back to my title. As a developer, if I don't have to rewrite all my code so that it'll work on IE, then it gives me more time to make things look and work better for all browsers. As much as I love Firefox, a good majority of the world still uses IE (albeit, there's still a huge percentage of IE6 users which is a bit discomforting) and developers spend most of their time getting pages to work for IE rather than the other browsers. With IE becoming standards compliant, developers will start to code their pages to be standards compliant, which will benefit me as a Firefox user.
As a side note, I managed to get my page to pass the W3C validator so my page is now standards compliant!