Neodymium magnets are very, very strong magnets, far stronger then any natural magnet. They are small and lightweight and used where these attributes count (like disk drives). You can use ones from the old drive, but you'll have problem with shape matching curved filter surface, also temperature range.
I use these:
http://cgi.ebay.com/Neodymium-XMOD-M...QQcmdZViewItem
Ordered 4 pairs and put on base of filter alternating poles (N-S-N-S-N-S-N-S). Because of small size and curved shape, they stick well with two straight edges on filter wall; close enough that you can then screw the filter on and there are no clearance problems with crankcase well. When you look at filter from the top, you'll see series of silver bumps circling outer surface. There is no problem to put filter wrench on top of filter.
For 20 bucks you have increased engine protection - no-brainer for me.
