We've started using the client review page and found it very handy for giving previews.
One thing though is that the even logs don't have the full set of information we'd like. For regular users, the event logs track when versions are seen, but this doesn't show up for client users. It'd be very handy if it did so that we'd know what clients had and hadn't seen. I know that there's an event logged when thumbnails are seen in emails, but that doesn't really help with knowing whether or not a client looked at the version in a playlist.
Our main concern with this is knowing that a client opened the page of a particular version in the playlist. A way to track that they've seen it without requiring them to leave a comment to that effect.
Also, when a client downloads a version, on the event created by that, the "Link" field contains the client themself instead of the version. The version id is present in the event summary, but that means you have to just manually find which version that is. It also means you can't link through to other fields on the version, since that's not the actual event's link.
If these could be changed it would make the logs for client review much more useful.