I have been using Google Calendar for a couple of years. I love it for a variety of reasons. It lets my family & friends see when is good to come visit, keeps track of things I don't really want on my work calendar (things like "yoga class" or "meet Laura for tapas"), and nicely drops in notices of events on other sites I might be interested in (Last.fm's recommendations are always right on the money - I love it.).
Last week I installed the Google/Outlook sync application. While I like keeping work and non-work events separate, I often need to see them both so I don't double-book myself. So I set it up to send my Outlook events to Google. It quickly started driving me crazy, popping up reminders every few minutes of events, most of which were incredibly old. I thought eventually it would cycle through all my old events and be finished, but it didn't seem to; events kept popping up repeatedly. It got distracting and after a couple of days I uninstalled it. Bummer, because I was really excited about finally having them synched.
I took this as a sign to finally try Windows Live Calendar. Windows Live Calendar went into public beta last November. When I first looked at it, a long, long time ago, I remember thinking, "Uh, not fully featured enough for me yet...I'll give them some time."
This time when I went to check it out, I was quite 
surprised and pleased! There is a lot of functionality, and some of the things I love about Google Calendar are there now, like importing calendars in ics formats, sharing with friends and family, and drag-and-drop.
Something I like even better is Windows Live Calendar's "Add an event" functionality. In Google Calendar, you can add a minimal amount of information when you first add an event by dragging a section of the calendar. Often I have to jump to a separate page to add more information. With Windows Live Calendar, I can do most of it inline without any new browser navigation, which is nice.
I'm talking specifically about adding events by clicking on the calendar here. One thing Google did quite nicely was its slick "Quick Add" option, where you could write something like "Lunch with Beth at Aya 1pm tomorrow" and it would add it in the right section, doing a bit of cool language processing. It was never mission critical for me, in fact I rarely used it. But I just thought it was a really well-done part of their UI.
I like Windows Live Calendar's Sharing ability a lot better. It's much more straightforward, and I can do things like publish to a hidden URL, where only people I send the links to can view as HTML (without having to log in, or use their Windows Live ID or anything). I can also share it with people and give them edit permissions on one or more of my calendars.
My most important test of calendaring features is the Last.fm Recommended events. If my calendar can import that no problem, then I'm all set. This was a little clunky in WL Calendar. I couldn't paste the http link in the textbox, I actually had to click the "Browse" button and paste the link there. And it took me a while to figure all of this out because it would freeze for a bit if there was text in the textbox when you click "Browse." Anyway, once that happened, it told me 7 out of 14 events were added, but there were problems with some of the events I imported. So I'm not sure what that's about. I am sending mail to the product team to find out what the deal is, and hopefully I'll have info to post on that shortly.
In the meantime, I will keep beta testing this for a while and see how it goes. It's certainly a usable product, and if it can ease my synching calendar woes, then I will definitely be converted.
