I think the different rendering modes in IE8 is a serious defect. For example, when testing locally IE8 defaults to IE7 mode instead of IE8 standards mode. You physically have to go into the developer toolbar to switch it. My friend(who's a .Net developer) ran into this exact problem last week and couldn't understand why his site was failing in IE8, looked good in IE7, and worked well in FF & Safari. I've run into this problem more than enough times.
If people need to use a particular older browser for a very narrow application, then they should keep an installation of that browser around for that specific purpose.
Its the same idea with modular programming methods. I build my js in modules. My comment system is separate from my login system. In the last couple of days I have been updating the Facebook Connect logic in my login system and I haven't had to worry about updating logic in my comment code.
If people need to use a particular older browser for a very narrow application, then they should keep an installation of that browser around for that specific purpose.
Its the same idea with modular programming methods. I build my js in modules. My comment system is separate from my login system. In the last couple of days I have been updating the Facebook Connect logic in my login system and I haven't had to worry about updating logic in my comment code.