I will wait until the final version is in before making yes/no decision. However, there are several areas that currently concern me, Updates is one of them, I'd like more control, hope it comes once we are on the RTM version. I never use IE, so it is of little or no concern to me. However, if they come up with an ad-block adaptable browser, I'd give it a shot. I'd prefer not to have to install another browser, Chrome being my choice today.
I'm eager to check out Spartan just to know if you can run multiple instances of it, something that is currently impossible for a Metro/Modern/Universal/Store/<YouNameIt> app. Spoiler A little off-topic, but concerning "Metro": Well, they started this whole Windows Runtime API with Windows 8, now there's no going back. Looking at and thinking about it, the whole Windows development platform (consisting of Win32, .NET, and WinRT) has become a complete mess, due to the restrictions put upon each part of it. For example, if you write a traditional Win32 application, you cannot use certain WinRT APIs and vice versa. The same is true for .NET. The WinRT XAML stack is native but is only available to apps and lacks a lot of the features that make WPF really powerful, but WPF is pretty much done and will be phased out sooner or later in favor of WinRT, despite the recent announcements of the WPF team. Further, there's stuff in Win32 that is not available in WinRT/.NET and vice versa... Maybe in the long term, WinRT will go the route of .NET - desperately trying to replace Win32 but finding it a hard nut to crack. But who knows. I just can't imagine anybody writing a serious application based on it.
I find it interesting that MS is pursuing a clean new browser project. It could turn out nice, it has to be to get the discerning users that currently use FF or Chrome, etc. Using FF Beta stream here (both 32 and 64 bit versions), after losing patience with Chrome's unbound appetite for memory and resources. Not looking back to Chrome, but looking forward to trying out Spartan. And yes, it will need to have extensions, like the competition.