This is coming from someone who's used Firefox exclusive for the past 5-6 years - IE10 is good. So much so that I've switched my default browser from FF to IE10. I've still got FF & Chrome installed for testing purposes, but the majority of my work is in IE10 these days. I do miss the FF extensions like AdBlockPlus, Flashblock, etc.
This is the desktop version of IE10 in Windows8 - I've had no need to use the metro version for anything serious yet. I've played with it, but that's about it.
When I first switched to Win8 RTM about 3 months ago, FF performance on the desktop was absolutely the worst thing you've ever experienced. Slow as a wet week, and it's memory usage was abysmal. IE10 was blindingly quick. That was a large motivator for me to change. The latest version of FF has fixed most of those issues though, and is now quite stable (still useless with it's memory allocation - it's FF after all - but at least it's improved). The less said about Chrome the better.
Some issues I have with IE10:
* It's not compatible with MS Dynamics CRM. Some of it works, but the admin stuff just breaks badly. To be fair this is more of a black mark against the Dynamics team, but it's still annoying since that's been a large part of my life lately. Waiting patiently for the Dec update for Dynamics that promised cross-browser compatibility (hurray - welcome to 1997).
* It mucks up on a large number of AJAX sites. IE9 could cope with these particular sites, but IE10 just drops it's bundle and you need to manually force it into Compat mode. Example : carpoint.com.au. Go there, select a manufacturer from the drop-down, and then wait while IE10 does *nothing*. Instead of populating the model drop-down, it just stalls. Once you slot it into Compat mode for that site it all works, it's just a lot slower to load a page and initialise all the JS.
* I've got some sort of java/javascript issue with IE10, that is most evident on forums like this. When typing into a text box, a few sentences are fine but once you go past a paragraph or two it all slows right down. it doesn't break, but you can type a whole sentence before the first character pops up in the text box. I've not been able to narrow down what causes it, it's reasonably intermittent, and the latest JVM update may even have resolved it. It's annoying enough that I usually open forum posts into FF so that I can reply there. Not sure if it's just me though - I suspect it may just be this laptop.
* Same as every other version of IE, you've got to exit the browser to change certain settings such as which proxy to use. If you change it on the fly, IE will stubbornly continue to use the old setting. It must only load the settings from the registry on startup. If FF, et al, can have this sorted by now, surely IE can. Likewise, clearing your cache/cookies doesn't completely take effect until you restart the browser - annoying when you're troubleshooting cookie-based authentication systems.
As mentioned above though, it's clearly the best version of IE yet, and is still considerably faster to start up and get working compared to either FF or Chrome. Highly recommended to give it a whirl.
Cheers,
Matto