Just to echo what other posters have said, I got back on Tuesday after a brief trip and there's very little disruption to speak of.
We stayed in Reykjavik and went as far east as Vik (well, almost to Vik) and also explored the Snaefellsnes Peninsula. We encountered no road closures (beyond closures for winter, which as far as I'm aware is normal) and certainly the ring road was open even near the volcano.
There's a section of gravel - tarmac - gravel - tarmac where I think they broke the ringroad to let water through, but slowing down for that probably only adds five minutes to your journey.
The most noticeable thing for us was the emptiness of the two hotels we stayed in. Not sure if that's normal for this time of year. Oh, and Keflavik Airport seems to be closing every now and then as the ash cloud moves about, so check your flights. I think they've been using Akureyri airport as an alternative, so you might be looking at a lengthy bus ride when you arrive / leave the country.
Have a good trip - it was my first and I can't recall being so impressed by a new place.
Cheers,
John.