We (three dutch bikers) were send back to Tunesia early januari this year. We had our visa arranged by a travelagency in Holland which, like almost the rest of the world, didn't know Libya changed regulations 1-1-2001.
By now it looks like that it is official that you will need a guide with you from border back to border. Also bikers have to be in a group with cars.
Havent heard of people getting deeper into the desert without a guide. But transit from Tunesia to Egypte or 2WD cars seem to get through sometimes.
Its going to be hard to get into Libya now without a guide. Maybe some creative travel agency will figure out a way to get you in officially with a guide only to help you in and out of the country. Not sure what will happen if they stop you without a guide in the south.
As I still want to go back there one day, so please keep me and this bulletin-board informed of your progress.