I've heard it said that one should not use synthetic oil during break-in, because it can impair proper wear-in of the rings and other moving parts.

Well, my daughter (lucky gal) just bought a new 2007 Pontiac Solstice, and lo and behold, the car comes equipped with synthetic oil from the factory. Corvettes, Vipers, and many others do too!

So, this must mean that, at least for some new engines, that it's perfectly OK to run synthetic oils from day one. Does this apply to motorcycle engines? Hard to say. I assume that it depends on the manufacturing methods used, but these days, I assume most all automotive engines (including motorcycles, of course) use similar methods and are manufactured to close tolerances and require less rigorous break-ins than did engines made when I was a wee lad. So, the answer is: perhaps.
Enough of my uninformed rambling! What do the oil manufacturers say?

Mobil

Myth:

You should break in your engine with conventional oil, then switch to a synthetic oil like Mobil 1.

Reality:

You can start using Mobil 1 in new vehicles at any time, even in brand new vehicles. In fact, Mobil 1 is original equipment (it is installed at the factory) in:

• Acura RDX
• Aston Martin
• All Bentley Vehicles
• All Cadillac Vehicles
• Chevrolet Corvette C6 and Z06
• Chevrolet TrailBlazer SS
• Chrysler 300C SRT-8
• Cobalt SS S/C Coupe
• Dodge Caliber SRT-4, Charger SRT-8, and Magnum SRT-8
• Jeep Cherokee SRT-8
• Mercedes-Benz AMG Vehicles
• Mercedes SLR
• Mitsubishi Evolution
• Pontiac Solstice GXP
• All Porsche Vehicles
• Saturn Ion Red Line and Saturn Sky Red Line
• Viper SRT-10

One of the myths surrounding synthetic oils is that new engines require a break-in period with conventional oil. The fact is, current engine manufacturing technology does not require this break-in period. As indicated by the decisions of the engineers who design the high-performance cars listed above, Mobil 1 can be used starting the day you drive the car off the showroom floor.

- http://www.mobiloil.com/USA-English/MotorOil/Synthetics/Myths.aspx

Redline Oil

Can I break-in my engine on Red Line Oil?

We recommend using petroleum 10w30 motor oil on break in to ensure proper piston ring seating. If you allow 1500 to 2000 miles in a street engine or 20 to 30 minutes on the dyno at low rpm, the rings will have had sufficient time to seat and the high initial break-in wear will have occurred.

- http://www.redlineoil.com/tech_faq.asp

AMSOIL

Q. I heard that new cars require a break in period with petroleum before you switch them to synthetic. How long should this break in period be?

A. AMSOIL Synthetic Motor Oil can be used during break-in trouble free. In fact, vehicles such as Dodge Viper and Chevrolet Corvette come factory filled with synthetic oil.

Since most new vehicles come filled with petroleum oil, it only makes good sense to change to AMSOIL at the first scheduled oil change interval. New engine components generate high levels of wear metals and can contain contaminants from assembly. By allowing the engine to operate with the petroleum oil until the first oil/filter change interval, the wear metals and contaminants are removed prior to installing AMSOIL.
- http://www.amsoil.com/faqs/faq1.aspx