I have been using the platform preview version on and off for a while. Must say impressed. But IE still fixing many things.
Also, WP and many,many themes have issues with IE 10 because of having IE specific css/js and other logic. Unfortunately many of these changes turn out wrong in IE 10.
For example, my base wp and SP theme have no issue in IE 10.
When IE 10 releases we will support it and be dropping IE 8 official support (all current will remain but stop testing new stuff). Hopefully IE will be a real browser this time. We currently spend way more time getting into work than getting base stuff to work on all other browsers. They are called standards for a reason MS.
Anyways, all that to say when IE 10 releases final, we will begin compatibility testing. I remember working that early on IE 9 and then a change the blast week invalidated that work. But will be bumpy road until wp and wp themes also support. Sad we even have to have these discussions – routinely update other browsers without even thinking about this.
As to signatures, you mentioned size, but not sure what you meant. Did you adjust the max sig height passed to the template tag?