My experience with LR is extremely limited and apparently should remain so. The comments below are of a general nature.
When you look through shots from a shooting session, the least important aspect has to be building previews for each and every file, and catalogue them. What one needs is the ability to go quickly through the file collection and if necessary, check those [few] files that hold a promise of further processing. Only the checked files should be worthy of "importing" and maybe renamed after specified criteria by the user and/or EXIF information. Thus, some vestiges of a functional file handling system have to be present. This is where PhotoNinja in its current incarnation fails badly.
I have little faith in monolithic applications so look instead for an optimised free-standing photo viewer to sort the session shots. Irfanview has a good reputation, but obviously there are more candidates.