Had my 66c since April 2013 and did little to no frame maintenance until recently. I never thought about not riding it in any conditions was very lazy with the jet wash, although not negligent. I recently noticed a creak, which turned out to be the x9 clutch, which can bind and 'snap' release sending a small shock through the frame, which feels like pivot bearing binding. Whilst I was looking at this I stripped the frame and examined the bearings anyway, I had started so I thought I should finish!
Link pivot bearings were all OK but pretty much in need of some new grease. The switch link bearings were covered in grit and gunk and needed some heavyweight cleaning. I ordered new switch link bearings, £26.95 delivered from yetifan.com, and packed the old one's with new grease having cleaned them first. I rode the newly greased machine and it felt much plusher and buttery, more like how I remember it was when new. I haven't put the new bearings in yet. I don't use the jet wash at trail center rides now, I take it home and gently hose the bike down. Gets it just as clean and I can still see the tell tale signs of grease around the edges of the bearings.
Yeti recommend the option of leaving the O Rings that 'seal' the switch bearing out in UK conditions as this allows them to drain when water and grime penetrate. In summary, great bike but be prepared to put in some maintenance. I am planning Switch regrease every month and full bearing regrease every 3 months or thereabouts based on 10 hours riding a week in moderate conditions. If you are a twice weekly rider and reluctant mechanic like I can be when busy I would estimate budgeting on a switch bearing set every 6-9 months and full bearings rebuild (£120) every 12-18 months.I think you could get double that with some care and attention.
This is obviously my own observation based on my own experience, I ride quite agressively, like jumps with air, use all of the suspension but am light on the bike and weigh around 70KG. I do trips to trail centers, Coed Y Brenin etc, on weekends and ride local trails during the week in all weathers.
I personally think that I should get more bearing performance longevity if I maintained the bike better, the high purchase price doesn't include any substantial after care unfortunately. However it does seem odd that there is no warrantee on bearing life or maintainance friendly grease ports to pump into such as Santa Cruz employ.