The only exception to the fork rule is early Rebas and Revelations. Rock Shox had an O ring on the gate dial (the gold knob on top of the blue compression knob) that was a bit feeble, and consequently a little oil used to weep out. Not a big deal, except that the oil cart it was leaking from isn’t that big itself, and oddness occurred (according to TF Tuned) if too much was lost. I had three Reba-based forks at the time with the problem, and none of them exhibited aforementioned oddness, although I did end up storing them wheels down.
I currently store four mountain bikes front wheel up in a shed. Nary a problem, but I should say that the nice cheap hooks from Wickes, B&Q and the rest are a little narrow for bigger tyres or rims – I’ve got a pair of Easton Havocs with 2.25 Advantages on them, and that can be a tight squeeze. It’s also easy to knock the rubber coating off the tips of the hooks, so watch you don’t end up scoring your rims. That said, a replacement hook is a quid…