Probably the most important missing feature in Google SSL Search was image search. Now this feature is available, but there's a drawback: the page that shows a bigger image preview doesn't use SSL.
Google's encrypted flavor supports most of the features of the regular Google site. The left side of the navigation bar is still missing, you can't use Google Instant and the Wonder Wheel, but hopefully these features will be added in the near future.
Google Chrome has recently implemented a feature called SSL False Start which "reduces the latency of a SSL handshake by 30%". SSL sites load slower and one of the reasons is that SSL handshakes are more CPU intensive, use more network round-trips and more packets.