I've used varifocal glasses for everything including trials and mountain biking, with no problem whatsoever for several years now.
I got used to them fairly easy, as others complained they had difficulty climbing stairs and such.
The same goes for the bifocal glasses I use at work.
The only problem I have, is adjusting to my sport glasses wich are single distant focus. They make me slightly dizzy when looking at obstacles close by. It takes about 15 minutes to get used to them.
I've tried contact lenses but couldn't get used to them, to much irritation.
I'm hope I can get my eyes "lasered" one day, when my eyesight doesn't deteriorate anymore.