I have had this macbook w/leopard for about 1.5 months and have seen this one problem a few times.
When shutting down I git the circular loading ring bottom third of screen and it just sits there till I hard press the on/off button to get tit to shutdown. I do not have any problems when powering up after this.
I have no idea where the repair tools or diagnostics are on this machine and will start looking but was wanting to see if anyone may have insights on this. No errors or other messages follow.