I run it 24/7 on two laptops - both XP SP2 - without any problems...

I'm just downloading that now - it looks good on their website.  Must say that I think the contact management in The Bat! is pretty good (it was shifting from Outlook to The Bat! for email that prompted me to want to drop Outlook and explore other calendar options). 

jpfx: there is a beta of EPIM 1.6 out now, which at least allows you to turn off the clock.  I would really like it if the whole layout were more configurable - I don't like where the mini calendar is on the right, but there's nothing you can do to move it...  Also, EPIM runs quite heavy - it sits at around 20 meg even when it's shrunk to the tray, whereas Calendarscope comes in under 2 meg.

zridling: I've trying the full version of TimeCalendar at the moment, and it's lightweight and quick and nice to look at, but for me it's hobbled by not being able to synchronise with PocketPC - Calendarscope can do this, EPIM has it in development.  Also, like the current version of EPIM (but not the beta) it only prints in black and white.  The author of TimeCalendar told me he is about to launch a completely new version, so maybe it'll be able to sync and print in colour then.