I don't have a problem with running any sleeved bearing fans horz, but I always set them up so the hubs point down or pulling air out of the case. I've been running 3 YL's like that in my main rig for over a year, and they are still smooth as silk. But I have had sleeved fans make noise while running with the hubs pointing up, but I've never had one go bad on me.
That being said, I've never had a YL or Zalman ZM-F3 fan go out on me regardless of how they're orientated, and I've had several of each in continuous service for years. Based on my direct experience, the necessity to run a bearing based fan is highly over rated, and I've never found a bearing based fan run as quiet as a sleeved based fan as far as mechanical noise is concerned. But that's a highly subjective thing when it comes to noise, so let your own ears be the judge.
andyc