Just had a go through the hosted demo, and it seemed very nice, if a bit slow. That may be due to the slight lag from Ajax though.
I sent myself an email with the message as follows.
Hoping to test out the date hover function.Hi Paul, OK then the 3rd October at 14.30 then ?
When the email arrived in my inbox the date above was not highlighted
However I replied to the email, and then went to the sent box to view the sent mail, I noticed that my original message had the date highlighted and when hovered over it popped up the calendar function. Not very handy when I want to add the appointment to my calendar.