Accoring to a security expert, they contain lots of bugs which can be exploited by virus makers. Some of the bugs are unfixable and cannot be worked around (a software patch can't fix it). The only way they could fix some of the problems is to do a recall and replace everyone's processor. So I would wait to buy until they got everything worked out...
Here are some links:
http://hardware.slashdot.org/hardwar.../1124256.shtml
http://marc.info/?l=openbsd-misc&m=118296441702631