I'm working with the Amazon Simple DB web service. It stores everything in strings as such I needed to store a DateTime in ISO 8601 format for later sorting the strings in correct order. The frameworks has at least three formating strings. Either s or u or o. The s format seems like a good choice as it's called the sortable format. However it doesn't store any sub second data or timezone info. The u format is s in universal time, but still lacks the sub second data. Lastly the o format for round trip stores all the DateTime info in ISO 8601 format and should remain sortable as long as all dates are stored in the same time zone. MSDN DateTime format strings

Here's more good info on storing data as a string in ways that are sortable later and useful Simple DB info.

http://docs.amazonwebservices.com/AmazonSimpleDB/2007-11-07/GettingStartedGuide/
http://docs.amazonwebservices.com/AmazonSimpleDB/2007-11-07/DeveloperGuide/
http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1231&categoryID=152
http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1232&categoryID=152