My boss recently installed IE8 Beta 2 just to see what would happen. Of course he decided to go and navigate to our application which resulted in the usual phone call we all dread:
Boss: So Josh I just installed IE8.
Me: Huh huh, and how'd it go?
Boss: Our site looks like crap...
And I am sure you can imagine the rest of the conversation. Our site is optimized for IE7 standards mode, which isn't exactly compatible with IE8 standards mode.
There are a couple of ways we can resolve this. We can invest the time to bring our site up to IE8 standards mode compliance (and in the process hopefully add support for the other browsers which we don't support); however, this takes time which costs money which new startup companies don't always have the luxury of.
Another solution is for the site to lock in to a particular rendering engine. This is a brilliant addition to the architechure of IE, and I hope other browsers follow suit. Its the same concept of being able to lock in your client application to a particular version of .net.
I won't regurgitate how to do this. A really good article is available here.