Some good reading:
(lately I can't get this page to open!)
"Car" oils are a no go, for a couple of reasons. Since 1993 they have had a downgraded anti-wear additive package (ZDDP) because of catalytic converters, and the ZDDP has been replaced with the inorganic friction modifier moly, which will make your wet clutch slip. Use to be you could run a "diesel" oil and still get a descent additive package, but they too have now been downgraded because of cat converters.
It's pretty simple.....you won't go wrong if you run a motorcycle specific oil that is API SG/JASO MA. The SG insures that it has pre-1993 levels of ZDDP, and the MA insures that it will not make your wet clutch slip. Beyond that, there are three different types of synthetics, and the best of the three are the esters.
I like all of Maxima's oils, becasue they have a monster additive package! Their Extra is an excellent ester based synthetic, but it is expensive!
If you want a performance oil that may net you a little extra torque and horsepower, yet still give you the unltimate in protection, then I would recommend Redline (motorcycle oil in the BLACK bottle), or Maxima Ultra or 530MX (for very cold weather). These all contain a new generation of organic friction modifiers that are wet clutch safe! This is the direction where the future of performance is headed, but these oils are expensive!!! (One note, even though Redline is JASO MB it is still wet clutch safe, so don't let that scare you off!)
All that said...you may look in your owner's manual and it says you can run car oil if it is not "energy conserving". In most parts of the world, it will be impossible to find a "motorcycle specific" oil, so "car" oil is better than no oil at all! Is it the best for your motorcycle...absolutely not, so if you are not forced to run it, find some motorcycle oil instead.