In reply to craig1983:
> I did this last night and when putting it back on, it took me half an hour of fiddling with the QR tension to get the wheel seated perfectly again where its not rubbing on the brake pads (hydraulic discs). I thought 'B*gger doing that every time!'
Something's not right here. The QR tension should not make any difference to the alignment of the wheel. With the bike upside down, the wheels should sit nicely in the dropouts and the disks rotate smoothly in the calipers. The QR basically clamps this position: the distance between the dropouts (the Over-Locknut-Distance) should be exactly the same for both hub and frame - down to the millimetre. If the QR tension is changing disk alignment by even a mm then something is wrong somewhere.
The alternative is that the pads moved when the wheels were off, but you said that you put the spacers in, so I don't know...
Anyway, IMO most bike racks are a faff - the only ones I've ever used which aren't are the towbar mounted ones. But if you have a small car they make life easier, and they also save the car upholstery after a muddy ride.