I think a good feature request is to have an OK button at the Order search page, instead of an "instant results as you type" approach.
I update about 20 to 30 orders statuses a day.
This requires me to search customer names etc.
For every character i type, cart66 executes a database query,
when i backspace, another query is performed.
So if you do not type a name very fast, you end up with an extreme amount of sql queries on your server.
The result was getting a "Size of a request header field exceeds server limit" error and could not access the backend of wordpress at all.
This is happening on a regular basis.