The ease of using it for my day-to-day work needs! It has made scheduling meetings incredibly simple as I can see who's free at any given time without having them email me back every single one individually (or worse send reminders). There are some minor glitches here or there but nothing that makes you stop what your doing - just something about how they display certain things sometimes when editing events doesn't quite match up 100% perfectly so its hard not have doubts like "oh no maybe this isn'g right" etc.. But overall great software all round :) Really helps make our jobs easier by making organising appointments very quick indeed!!