Please Look at: http://www.extjs.com/forum/showthread.php?t=5397
I reworked my previous http://www.yui-ext.com/forum/viewtopic.php?t=3645 example into a new form component called HistoryComboBox.
As with the previous example, it's far from perfect and more like a proof of concept.
See it in action here: http://ido.nl.eu.org/pir/
The database contains over 200k of records, that should be enough to demonstrate a very big record set
HistoryComboBox currently has the following options:
maxInHistory - How many entries to remember (default=10)
rememberOn - When should an entry be rememberd, options: 'enter' or 'all' (default='enter')
fixed bug with paging and filtering, thanks Belgabor![/edit]