Was scratching my head for a few minutes when a bound column in a grid in my ASP.Net page didn’t format correctly, for future reference and in case it can help some one here is the solution:

Set your DataFormatString to the right format, for example I set mine to {0:dd/MM/yyyy} to show my date correctly and then (and this is the secret trick) you have to set HtmlEncode to false on the column and your column should display correctly.

Weird that I could only find this after a few minutes of Googling, its not in the help as far as I could see.