I've got a vive and at this point I've probably spent around 40 hours in it, including a few multi-hour sessions. Before that I played with an early Rift dev kit for several days.
The biggest issue is when the world moves without you - Windlands is a big culprit here. In general standing and using controller locomotion so far has been a recipe for nausea.
But outside of that, so far everyone who has used my unit (and that's about 20 some people currently) has had a blast. No cases of simulator sickness (and I've only seen two reports of that in the community as a whole so far) and no nausea other than an initial misattempt with Windlands.
Sorry, VR is probably here to stay, though whether it goes mainstream will be about whether or not the price can drop quickly.