Couple of suggestions, hope they are useful
Right click on parent directory button, brings you to the root of the server.
Option to define how to sort on folders AND files. Eg I would like to sort folders by modification date and files by name
Define max of concurrent logins and downloads for a ftp in global settings and an option on each bookmarked ftp to use global setting or customize for the single site.
Tabs of course, but I see this have mentioned lots of times and are expected in what? Version 5?