I'm running MenuCalendarClock's version 4.1.2 on OS X 10.6.7, with Spaces enabled (I chose to have the app displayed on every space).
MenuCalendarClock sits in your menubar as a small calendar icon (you can choose between 3 icon alternatives), and optionally also replaces the system clock (you can customize the clock's time format, font and color). There's a dock icon as well, which you can opt to hide, but the developer doesn't recommend it.
Upon clicking the menubar icon (or alternatively, you can set a hotkey), a small calendar pops up beneath the menubar, displaying the current month. The display preferences allow you various adjustments (like weeks starting on Mondays, tooltips, etc... There's an option to show Sundays in red, but I haven't found such option for Saturdays).
If you click on a day once, a Schedule slides from the bottom of the calendar, displaying said day's events. You can click the options' cogwheel (bottom right beneath the calendar) to add an event or a to-do item to the selected day.
Double-clicking a day opens iCal in month view but you can check an option to open iCal in day view.
Arrows at the bottom left of the calendar allow you to go backwards/forward between months, or go to the present day. Bottom right, there's an options "cogwheel" (mentioned above), to-do items button and close button.
MenuCalendarClock syncs with iCal. You can select which iCal calendars to sync with. There's an option to add a Birthdays calendar (you need to create an extra iCal calendar).
All in all, I like the app's compact look, and iCal syncing went fine for me.
I do have to note, though, that the transaction did not go smoothly for me. Despite completing payment, the e-commerce platform I'd been transferred to to make the purchase (I think it was one of Digital River's) presented an error instead of supplying me with a license code. I emailed the developer (Objectpark) using the email address supplied by the e-commerce service -- support AT objectpark DOT net -- but the email bounced ("Recipient address rejected"). So I went to Objectpark's website, found there a different email address for support, and emailed the developer again, this time to the new address. That email was likely delivered (at least, I didn't get a "delivery failed" notification), but the developer hasn't responded. So, I emailed the e-commerce platform's customers service, and after about 2 or 3 emails, they finally emailed me the license code. If you purchase the software, I hope the transaction goes smoother for you.