It will be interesting if the literals "From" and "To" in the filter area of the GridDatetimecolumn take their values from resources, as all other controls inside RadGrid. This way will be easier to localize the grid.

Having Paging enabled, the Column Aggregates should be calculated based on the data from all of the group's items, even if the group is spread over several pages.

Currently, only the data from the visible items on the current page are calculated. 

When Grouping on an Integer value, the groups are not ordering correctly. i.e. if you group on values {864, 1455, 1494}, the actual order comes out as {1455, 1494, 864}.

Ordering on the same data, but converted to a string and padded to the left with zeros resolves this issue.

It is possible to have "{4} | Page {0} of {1}, items {2} to {3} of {5}" (all 6 parameters) for PagerTextFormat, but not just "items {2} to {3} of {5}".