It is pretty well agreed on that its not that 'ard boyz are neccessarily bad, it's just that with the new codex, boyz got a significant point reduction making 'ard boyz a less viable choice. Although I have never used them and do not have any 'ard boy models, I still like them.
Due to their points cost, I see them best utilized in lists which contain large amounts of boyz. In an all footslogging list their use seems suicidal since they will obviously be targeted right off the bat, but I think in speed freak or semi-mechanized lists they could prove to be relatively effective. Because of their up-armored nature, the place of a 'shock troop' seems to be best fitting. Normally Nobz accomplish this, but at a steep cost. a regular 'ard boy costs half of a normal 'shirt-save' nob and costs a third as much as an 'ard nob with cybork.
In the mechanized aspect, a trukk full of ard boyz are capable of making a hard hitting charge like most trukk squads, but will soak up return damage much better. I would use them as a means to whiddle down a much tougher opponent who normally does not want to be in close combat.
In the semi-mechanized list, I think ard boyz could be used to a much greater extent. If you have a large amount of boyz slogging up the field, a battlewagon full of ard boyz could be just what your list needs. They provide the shock troop resiliency nobz have at that cheaper price. Using them to tie up frontline enemy units could be brutal. Imagine your ard boyz in a wagon make a second turn rush to engage front enemy units. With the ard boyz resiliency, there is a large chance they could tie up the enemy long enough for your main footslogging force to arrive.
My final thoughts are making an uber-resilient squad by attaching them to the Mad Dok. Granted you wont have much control over where they roam, but with 4+/4+ saves they could do a world of hurt at the same points cost as a regular 'ard boyz squad.
However, since they have almost a double cost of a normal boy, numbers I believe will be crucial to the success of a mob of 'ard boyz. Remember they attack like regular boyz, so they are going to need a significant amount of back-up.
Just my initial thoughts, since I have never used a squad of them.