I just got a copy of the new Lightroom 4 for Windows in and upgraded my catalog.  Right now my catalog is sitting around 100k images.  The catalog update went well and wasn’t a problem.  I’ve not had too much time to go through the Develop module yet to see all the new changes.  I’ve been watching some of the podcasts from PhotoshopUserTV and learning about the new features.  It has support now for video which is nice as well as overall enhancements in several areas.