In work I am constantly being sent meeting requests by managers who are using Outlook on Windows. But I am using Thunderbird on Linux, which can't make sense of these meeting requests so simply displays the VCalendar meta data in all of its ugliness by default.
Recently I discovered that I can use Lightning from Mozilla, which integrates the Mozilla Sunbird calendar application with Mozilla Thunderbird to offer some very nice features, including the ability to create a calendar event based on a meeting invitation, including those coming from Outlook:
Well worth checking out by Thunderbird users on all platforms. Mozilla really are producing some great software these days!
Updated 2021 : note that the above post was originally published in 2008, but is left here for archival purposes. It seems Thunderbird and Lightning are still going strong!