Recently I had the issue of a Sharepoint Calendar showing some weird times for the appointments. It turns out that they are all off by three hours, putting the calendar in a different time zone.
It took me a few minutes to find the answer but there are a couple of places to change the time zones;
1) a global setting for all new sites that are created:
Thanks to Liedong(Ken) Zheng at http://littletalk.wordpress.com/2010/10/18/central-administration-regional-settings-in-sharepoint-2010/ for pointing this one out. Opening the Central Admin console on the server, you can navigate to App Management > Web Apps > Manage Web Applications. Select the site and click the Change Settings in the ribbon bar, and pick General Settings.
2) at a user level:
Thanks to the Programming 4 Us site - http://mscerts.programming4.us/sharepoint/sharepoint%202010%20%20%20change%20my%20regional%20settings.aspx
Click the user name to get the user menu, pick My Settings and change the Time Zone
3) at a site level:
Thanks to Amol Ghuge over at http://sharepointknowledgebase.blogspot.com/2011/03/regional-settings-in-sharepoint.html.
Click Site Actions menu > Site Settings and then under the Site Administration heading, pick Regional Settings.
For me, it was number 3 that I had to adjust.