With the right fit, I can't imagine them falling out while running but not being able to put them over-ear would be a drawback I think. They are plenty light so it could work. I also ordered the younger siblings in the series, the XB30 and XB60 because I love the XB90's so much. Those have smaller 13.5mm drivers but I believe you still can't put them over-ear because of the same form factor but I'll report back. Still, they are not very cheap so maybe something like the JVC FX40 for working out and XB90 for everything else might make sense.
How FX40 or other cheaper alternatives fare for sports? Can they be worn over the ear, microphonics? I assume you had them all, so any further comments would be grateful.