mmcfine: Even though not really an upgrade I got LR4 for it's video archiving. this alone is a great way to archive and manage all the digital assets. You can do some simple trimming and color corrections to video clips but LR is not for that and hope Adobe won't make LR a mammoth as they so often do with other products. All in all, it runs the same as all other LR versions. I am running LR4 on a mid 08 MBP and it's OK.If you need LR for it's core capabilities then you can skip this version.
Core capabilities are vastly improved from 3 to 4