We just did the 4.61 upgrade a couple of weeks ago. It has worked really well, the client is much faster and does not "lock up" as much. It also has a better list of supported features and an enhanced MAC agent over 4.16. There are also improvements in the X64 versions of windows it now can do true remediation.
The only downside I could see although I doubt this is a big issue would be you no longer get Win 9X or NT4 support.
