I am looking at setting up calendar sharing with colleagues who all work individually at different locations.  One option appears to be the share calendar function (via Windows Live login) in outlook - does anyone know how secure/insecure this is likely to be as the calendars will have personal information on them?  It appears as though the only people to have access are the ones you choose to share it with.

The other free method was google standard apps, but this is definitely not encrypted when I am viewing the calendar on my computer.  Google premier apps appears secure but costs USD50/user/year, which appears comparable to all of the other paid secure calendar sharing options I have found so far.

If anyone has any other ideas on a good way to share the calendars securely will be appreciated.   Needs to be web based as no server etc.