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.
I recommend you explore some real DAM software. LR is mediocre DAM at best. Some possibly better are for example Canto cumulus, Extensis portfolio, iView MediaPro or Phase One Media Pro. Some of these are image managers, some real asset managers, which can manage all your documents (inc. doc, pdf, avi etc).
Those other programs have minimal or no image/video editing possibilities, but their asset management features rock.
ISO 6400 says EXIF