When using the client-side resizeToFit() method of the RadGrid to automatically adjust a column's width it seems to cache the value (the computed width). If i alter on add contents to a column's header and then re-run resizeToFit() the column doesn't fit to the new contents.
I would like an option to reset the cache, maybe with an optional parameter to the resizeToFit() method.

It would be nice if you provided the same level of documentation on server side programming as you do on client side programming. Specifically I suggest you include some documentation on finding and manipulating controls on the itemdatabound event. Currently the only source for this information is in your forums and most of it consists of try this, if that doesn't work than try that. This is very frustrating because server side programming on RadGrid is substantially different than in Microsoft Grid Control.

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. 

The selector area of the dragging to select automatically goes all the way to the left; could that be changed so that the area shows up only from where the user clicked to where the cursor goes, like Windows Explorer? (see attached image)

You can use the following temporary workaround in order to avoid the problem:
1. Attach OnGridCreated event handler:
    ...
    <ClientSettings>
         <ClientEvents OnGridCreated="onGridCreated" />
    </ClientSettings>
    ...

2. In the event handler configure the group header according to the number of visible columns in the grid:
          function onGridCreated(sender, args) {
              if ($telerik.isIE7) {
                  var visibleCount = sender.get_masterTableView()._getVisibleColumnsCount();
                  $telerik.$(".rgGroupHeader .rgGroupCol + td", sender.get_element()).attr("colspan", visibleCount);
              }
          }

Expose the MinValue and MaxValue properties from the GridNumericColumn RadNumericTextBox editor control, directly to the GridNumericColumn.