We have used Quark's UpAbsence for about 1 year now as our HR system with an excellent support team that really help us out when we had any doubts or questions! I can't say anything bad at all :) Sometimes it is hard to read through everything in order to know what your current status is etc., so it would probably be good if there was some kind of calendar where you could select what days / weeks are currently active, inactive, sick etc.
At least then you'd see which employees are currently working/absent without having to dig into each individual employee file. Overall, it works perfectly fine, but we were looking for something more advanced than just handling absence management (i.e. holiday booking), and this seemed like the best fit.