Per Processor Licensing
Although this is old news for SBSers (and not totally relevant)... now Microsoft has made public their policy of using Per Processor licensing (as opposed to Per Core). SBS 2003 is currently limited to 2 physical processors, but it can support 4 HyperThreading (virtual) processors. These are great news, because the experts predict that the chip engineering focus will change in the next couple of years to dual-core (instead of just higher transistor density) processors. Now Intel and AMD can build these chips without licensing concerns.
Check out the official statement from Microsoft