Well, we did the drive, but god wouldn't do it again. So bloody boring and lots of useless drivers out there. The road is ok though and its an easy drive. Nearly ran over some camels!
There are 2 border crossings - leaving UAE (after Hatta) and then you drive for a bit, then enter Oman. Leaving UAE is fine takes about 10 mins.
You have to get out, get your passport stamped and pay 20AED or something - Im on an Aussie passport & UAE resident visa so no hassles there. Then got to the Oman entrance and had to get out again and wait in a small-ish queue to fill out a form and another stamp (and another 20AED) on the passport. Took about 20-30 mins all up. No hassles at all. On the way back, just a stamp (and another 20AED) when you leave Oman, and they just wave you in at the UAE entry gate when you flash your resident visa as you drive past.
I love Muscat, but wouldn't do the drive again! Tiring and boring! We did it in 5 hours boths ways (left Dubai at 8am-ish Fri, arrived around 1 in Muscat) - yes we did the speed limit