expect Intel's FUD campaign to be don't invest (develope, buy) AMD64, it won't be compatible with Yamhill.
My feeling is that this would only work if the FUD starts soon--by Christmas at most--with actual shipping chips not more than 6 months later than that. More than a year and it starts to strain credibility, with more and more of the target market already validating/purchasing Hammers, along with more and more software support. The thing that gives me hope here is how easy it is, by all reports, to port to AMD64. There will be little reason not to for many software houses, and competition will force the holdouts to come around. And the classic FUD scenario is big megacorporation vs. dinky startup. AMD supplies a significant portion of the market, and its prestige has been increasing since the Athlon days. I'm not sure how effective a FUD-style campaign can be for that reason at least.
On the Intel side, the thing I'll be keeping my eye on is Itanium. Any signs of wavering committment, marketing changes, loss of any OEM support, etc. would all be possible Yamhill tracks.
But I'd be interested in your--or anyone else's--opinion on how long (and what) it will take for AMD64 to become entrenched and Yamhill-proof.