Version: 1.1 (using 4.1.3 (KDE 4.1.3) "release 52.2", KDE:KDE4:Factory:Desktop / openSUSE_11.0)
OS: Linux (i686) release 184.108.40.206-0.2-pae
dolphin does not autocomplete ftp URLs although I have used dophin several times with ftp connections.
The input box of KDE only can do a autocomplete for local files by reading the current directory content, there is no database behind which remembers the last entered URLs... But I fully agree to your request that this would be nice. I've set this issue as wishlist report.
*** Bug 178868 has been marked as a duplicate of this bug. ***
Resetting assignee to default as per bug #305719