I've used ASRock boards pretty much exclusively (the exception being Intel's own boards for Thin ITX boards) over the past 5 years in anything from servers (ESX, FileServers, Routers) through to desktops. My current rig is based around Asrock Z77 OC Formula and I've had absolutely no issues with it, completely rock stable unlike the Gigabyte Z77 Sniper that it replaced that blew! It's heavily overclocked as well, running 4.6/4.8ghz dependant on the outside temperature (damn having my office in a loft conversion!)
The only thing I don't like with them: BIOS updates seem slim and the drivers are typically out of date from their website. Easy to resolve though by going direct to the manufacturer.
ASRock did at one point have an image of cheap and nasty, which they were, but they've really come a hell of a long way and wouldn't hesitate to recommend them to anybody. Several friends also run them.
Actually I'm building a new ESX server based around Avoton, using ASRock's board.