What's diff between DVD-R and DVD+R

Different technology, basically.  More in-depth stuff here, otherwise, Google has a number of responses:

1). DVD-R:
Benefits: Better DVD playback compatibility within home DVD players.
Drawbacks: Older technology and less money behind the format means that they come out with faster media and burner technology slower. You will frequently see DVD burners that will support (for instance) 16X DVD+R and only 8X DVD-R.

DVD+R:
Benefits: Faster speeds, more innovations like Double Layer discs (8.5 GB)
Drawbacks: Will not play in some home DVD players. If you know your home DVD player will play DVD+Rs then there is no reason to not use them.

and:

2). The truth is that the two competing technologies use different formats. No single company "owns" DVD and both technologies have their "champions".

DVD-R/RW was developed by Pioneer. Based on CD-RW technology, it uses a similar pitch of the helix, mark length of the 'burn' for data, and rotation control. DVD-R/RW is supported by the DVD Forum, an industry-wide group of hardware and software developers, and computer peripheral manufacturers. The DVD-R format has been standardized in ECMA-279 by the Forum, but this is a private standard, not an 'industry' ISO standard like the CD-R/RW Red Book or Orange Book standard.

DVD+R/RW is also based on CD-RW technology. DVD+R/RW is supported by Sony, Philips, HP, Dell, Ricoh, Yamaha, and others, and has recently been endorsed by Microsoft. DVD+R/RW is not supported by the DVD Forum, but the Forum has no power to set industry standards, so it becomes a market-driven issue.

Technical Answer:
DVD+R is a dvd disc that allows multiple layers for one disc where as dvd-r only allows one layer. They will not compete to become the de Facto standard, because they are both here to stay. Multi layer DVD+R can allow extra capacity per disc than DVD-R hence its high cost!

and:

3). DVD-R (pronounced "DVD dash R" and DVD+R (pronounced "DVD plus R" are nearly identical formats. The discs look the same and are both supported by most DVD-ROM drives and DVD burners. The only difference between the formats is the way they determine the location of the laser beam on the disc. DVD-R discs use tiny marks along the grooves in the discs, called land prepits, to determine the laser position. DVD+R discs do not have land prepits, but instead measure the "wobble frequency" as the laser moves toward the outside of the disc.

The DVD-R format was developed by Pioneer and was released in the second half of 1997. DVD+R was developed by Sony and Philips and was introduced in 2002. Companies that support DVD-R include Pioneer, Toshiba, Hitachi, and Panasonic, while companies that support DVD+R include Sony, Philips, Hewlett-Packard, Ricoh, and Yamaha.

However, most of these companies now develop hybrid DVD drives that support both DVD-R and DVD+R formats. They are known as DVD±R or DVD±RW drives. When looking for media for your DVD drive, make sure it ends in "-R" if you have a DVD-R drive or "+R" if you have a DVD+R drive. If you have a DVD±R drive, you can use either format. DVD-R is still more popular than DVD+R, but since they are both widely supported, it should not matter which format you choose.