I think they lost focus a bit around v28. If it wasn’t for the oldskool style add-on I would have considered another default browser.
Looks like they got something right since 35 though – blur finally doesn’t need to be referring to an SVG filter anymore so that’s definitely an improvement.
I also suspect that even though in recent versions of IE the special filters don’t work anymore, they might still be functional when viewing the page from the actual legacy browser instead of compatibility mode. So it could be worth including them. Maybe I’ll have a look on my P3 500MHz with XP and IE8…
Edit – Yep