JCHERIAN  I am running Mac 10.5.8 on MacBookPro2,2 and MenuCalendarClock iCal 4.1 and I found that the program would consume all free memory. I logged into an admin account (that I rarely use) and found that there are no hangups or huge memory usage there. So I think there is an issue with how the program is reading the iCal file in my profile. Deleting my profile's preferences file net.objectpark.MenuCalendarClock.plist did not help. Reverting back to 4.0.0 did. I will submit this as an email to the developer though the web site http://www.objectpark.net/mcc.html indicates that they provide email support for registered users and I am only registered to 3.x and still undecided about upgrading to 4.x.  
(Version 4.1)