Ground plane are nice for various things. However they also have their culprits. You may do a little search and sure enough you will find some documentation on how to implement them the right way (assuming the author know how to )

You want to avoid unconnected islands, those may give you strange results and maybe screw up your whole design.

Take a bit of your time to read those bellow.
http://www.ce-mag.com/ce-mag.com/arc...103CE_028.html
http://www.radioing.com/eengineer/pcb-tips.html
http://www.amd.com/files/connectivit...86cc/22507.pdf

HTH