I have an ASROCK motherboard which I bought cheap to replace the lost board (I suspect ASROCK is just a division of ASUS) and so far no problems.
a division of ASUS, their aim is more towards the budget end of the market with ASUS "taking care"(!) of the high-end sector.
AsRock implement technologies usually before they hit mainstream integration, (eg. they were the first with eSATA ports), and use a variety of North/South bridges, not just nVidia/Intel/AMD, (eg. the ULi chipset on my old 939SLI32-eSATA2 outclassed nVidia's comparative chipset in terms of memory transfer rate - unfortunately nVidia bought out ULi, so another innovative product bites the dust).
So after saying they inhabit the cheap end of the market, I can also say that out of all the motherboards I have used, (low-end PCChips, high EPoX, mid-range Gigabyte, ANY
ASUS), that the two AsRock motherboards I currently have, (a K7S41GX and 939SLI32-eSATA2), neither have given me any
trouble at all over the last 2-3 years.
However, that said, I and all my friends currently run GigaByte motherboards in both high-end, (DQ6 series), and mid-range and apart from a few idiosyncrasies they've proven to be very stable and reliable - far ahead of ASUS motherboards.