There is no brand out there that is immune from this kind of thing. All the mechanics that i've talked to have generally told me that Merc, Yamaha and Evinrude are all good to deal with and take very similar steps in repairing their motors under warranty. I have no doubt that Yamaha will get you straightened out. I don't blame you for being ticked, but like I said, give them a chance to fix it. Aside from your 4-5 threads on BBC, I haven't seen any much talk about problems with the blown SHO motors. Most people seem to be thrilled with theirs, myself included (previously a Merc guy also).
Also before leaping back to Merc, you may want to talk to this guy and see how they handled his blown ProXS . . . .
http://www.bbcboards.net/zerot...22417