Okay let's clear things up a little.
DVD-R (dvd 'minus' r)
DVD+R (dvd 'plus' r)
The Pioneer drives, which are in every Superdrive Mac except for some of the new iMacs, can burn DVD-R, DVD-RW. DVD-R is what you would use for iDVD and such, and is supported by most consumer DVD players. But, even though Apple "does not support" DVD-RW, you can still burn DVD-RWs perfectly if you use third-party software, such as Roxio Toast. By the way, RW is ReWritable, so it means you can use the same disc over and over again, thus the higher price.
Now, some of the new iMacs have Sony drives, which in turn can burn DVD-R, DVD-RW, and DVD+R, DVD+RW. Now, this DVD+R is mainly used for computer data storage, and is supposedly superior to DVD-R. But, only new DVD players support it. Also, whether you can burn DVD+R is not tested yet...
Okay, didn't want to go into that much detail, but wanted to clear things up. Basically, if you want to use it for playing on a consumer DVD player, use DVD-Rs.
irmongoose