Yes, that can be a little tricky... Is there any query filtering you could apply to your list items prior to returning them to your form? I mean, if there are 10,000 list items, you don't need all of them, do you? Often, I'll store the display value for a dropdown in the form data as well - then you can show the selected value in a calculated value and give the user a button or something to switch back to a dropdown (and query for the "right" items prior to switching).
Hilary Stoupa
