Asus is hit and miss for me. They fill in a gray area in the middle. A few examples of how I see things with two companies each;
PCChips/Later BioStar - Transparent area; Rubbish, don't bother. At least not before the ECS buyout where some of their boards were actually decent, their only good boards prior to that were either by pure luck (M520) or were made by someone else (One that was a UMC reference design for the UM8498). Parts in the "transparent" area are usually dirt cheap and make promises they can't live up to, they use the worst parts possible.
ECS/ASRock (The latter is related to ASUS - owned by same company) - White area; Products which often show up in a white box which states "Pentium IV Motherboard" or similar. They are affordable and work as well as you could expect having promised very little on the box. The components are second-rate and they won't last as long as premium parts, but they'll get the job done and are OK for a consumer-grade box if you aren't doing anything heavy... For example, you want a Celeron system to go on Facebook. Occasionally something will perform better than expected like the ECS PF5 from a time when ECS went nuts and built awesome boards or some Envy24 cards from China which were identical to the M-Audio cards of the time but had better SNR at a lower price point. If you just want to game or go on the web these are by far the best choice when new as they are cheaper and will perform just as well as the more expensive parts in the gray area, you'll probably upgrade the machine long before the low-grade components become an issue.
ASUS/MSI - Gray area; Similar to the transparent area but with a higher price tag. These parts usually cost more and come in a flashy box, they use slightly better components but in reality offer little over their white area counterparts. The majority are cheap consumer parts and you're paying for a logo and a coat of paint to make you feel good. Employing one for workstation/server use is never a good idea. Sometimes a product in this category will work well like the ASUS AT3N7A-I which has an Intel Atom. The vast majority however, have short lifespans, stability issues and make more of those bold promises they will never reach. In short, the higher price tag makes these useless for anything and when companies from this area attempt to enter the Industrial or Server market they are usually ignored or laughed at.
SuperMicro/DFI - Black Area; These cost more, but you get what you pay for here. The warranty alone is longer than you'll probably need and the support if you take them up on it is much better. The device will likely be used by banks, data-centers and governments, all of which won't get you on another contract should they fail to live up to expectation. Strangely such devices usually come in a bland box which is clear on what the product is and what it is for - SuperO uses one box for many different boards - and the device looks plain. One look at the device will show you that only the best components are used, only the finest designers plan the layout and the soldering on its own is like a work of art. You will be hard pressed to find anything wrong with the device but the upgrade paths aren't always as long because they will not operate anything even CLOSE to where it will bring anything out of spec. Overall the best choice if you are doing something important.
My personal experience with ASUS has not been good, all but one ASUS product I have used has failed miserably. If it lasts long enough to be useful it has compatibility and stability problems but usually they just die without any warning. They are made of the cheapest materials possible, even if they use solid state caps they will be the worst ones available in Shenzhen at the time of its manufacture. Some of their more expensive parts are decent but at that cost (when new) one my as well fork out for proper hardware from Tyan/SuperO. Their cheaper parts leave you in a position where you may as well use their smaller subsidary ASRock of just buy an ECS who are a high volume maker - hence gray area.
Buying ASUS second hand is generally OK because all the crappy ones died years ago and mostly good ones remain, the P2B is one of their better boards and they work. They are certainly one of the better makers from the gray area and I'd take them over MSI any time... I can't think of MSI without thinking of the smell of burned electrolyte or the stability issues of the Core 2 Quad which were placed on top of the issues the CPU already had - but that's another story and isn't relevant to the thread. I just lean towards other makers if I can because of the experiences I have had personally, but I do use ASUS from time to time, old graphics cards usually it seems. In the case of my P3 I got it cheap years ago and I still have to rely on it, which is the only reason I really care now about the component quality as much as I do.
My opinions are sometimes controversial though and I understand that... You're looking at the guy who hates all Roland products, hates 3DFX, especially despises IBM and has no tolerance for Dell, Gateway or several other things other people seem to like. I have my reasons the same as anyone else. I also have high standards I think, sometimes unrealistic such as in the 3DFX argument - yeah, 3DFX's first card was garbage, but so was the solution from ATI and nVidia at the time, none meet the standards I set until years later. Just the way I think but that's enough rambling.