What Kenny said. I have a few large peices of cherry burl that has been drying for 2-3 years and I'm still not ready to cut it up, but they're BIG suckers! Not sure what I'll end up with, but it's worth a try.
To harvest the burls you cut down the tree/limb and cut above and below the burl. For really big ones you can chainsaw them in half vertically (ie parallel to how the tree was growing)
If you want to cut the burl up into smaller pieces, dip the entire oversize piece into wax! You need it to dry S-L-O-W-L-Y! There's a specialty wax carvers use that'll still allow it to dry... can't remember the name, but a quick search should find it.