I don't often look at the About SolidWorks dialog, but I recently needed to enter my serial number for something and I noticed that in addition to the 16 digits that have always been my serial number, there are now 8 more alpha-numeric digits added to it. I am using Office Professional and am at SP3.1. I'm not exactly sure when the extra digits were added but I suspect it was along with the product activation that happened with the upgrade from SP2.2 (I think) to SP3.1. I did need to enter all 24 digits of my serial number, the original 16 digits were not recognized as a valid serial number anymore.
Not a real problem, just thought it was a little odd that SW would change my serial number and not tell me about it.