Well, from what I have experienced and from what I have read on the forum from other owners, this is an issue on maybe 5% of the roads I travel on. 95% of the time it is fine. There is one stretch of the 5 fwy in so cal near Mission Viejo, where my truck does feel like a martini shaker. It is pretty violent. However, even with an unloaded bed, if I simply slow down to 70mph. Then it is fine. If I am driving 75 to 85 then it is shaking like the paint mixer at the local home depot. BTW, I have a reg cab, std bed, 5.7 w 20" limited wheels.
Would this stop me from buying one? No. Should Toyota have figured this out before the truck was release? Probably.
With any first production year vehicle you will have issues, big and small. This is the risk you take by being an early adopter. It's like all those folks who bought a 360 when it was first release and had their console crap out on them.
About 2 years ago a bought a 05 350Z. It was first released in 03, but considering all the early production year bugs it had, I waited 3 year to purchase a 05 model year Z. I still ended up taking it to the dealer 6 times for various issues.
The 06 Tacoma I had previously, was first released in 05 and if you go on any taco forum they had all sorts of issues also the first production year. My 06 Tacoma was flawless. First vehicle that I never took back to the dealer for minor adjustments. So most likely this and any other issues that crop up will be resolved in the coming years.
The irony of this is that the last year of production, when the vehicle looks dated and long on tooth is probably the most reliable version because they had the 4-5 years to sort through all the problems. This is the case with ALL manufacturers.
So go for an extended test drive and see if you can find a dealer close to your home or wherever you drive the most. Or if there is a Tundra owner near you who is gracious enough, ask them for a test ride and go drive your routine. Then you will know for sure. Just make sure to buy him/her lunch and gas!
Good luck.