LR History is wonderful for charting what you've done and allowing you to go back in time to re-work a photograph as well as for creating Snapshots after the fact and for the Before/After described above. Despite what Jeff says about it, some improvement would be helpful, however. (Really, a whole rewetting of code - Wow!) For example, after working with a single adjustment brush one may have quite a number of steps (e.g. building up from a 50% flow) of how a single brush may be implemented. It would be nice to be able to collapse those steps into one line and, later, if necessary, re-expand that collapsed "group".
BTW, it would also be helpful to be able to distinguish between the steps for each of multiple adjustment brushes (e.g. use a numbering system for each pin which would correspond to a numbering system in the History).
I've suggested this last point to Adobe - we'll see what they can come up with!