Do NOT try and do this directly - by that I mean inserting the disc, dragging your user Library to it, and clicking Burn Disc. This will NOT work! It'll fail midway through, and you'll have wasted a disc. Instead of doing that, make a disk image of your Library folder using Disk Utility, then either burn the image to the disc, or burn the image's contents using Disk Utility's burn image function. I learned this the hard way yesterday - fortunately, it was only 1 CD-R I wasted.