Dear community, you can do yourself a favour by replacing the build-in Wifi module with a better one. I ordered a Intel 5100 Wifi Link card for approx. 22 Euro,- (shipping included, at Amazon Germany).
Replacement was self explaining, easily done within five minutes. Now the Dell Mini 9 is instant online, no more waiting and waiting. Signal strength is significantly better even in places where it did not see any network before. And the best: Ubuntu 9.04 supports the card out-of-the-box, no proprietary drivers, no setup required at all.
Dell did a good job with the Mini 9 netbook, but took a wifi card far too cheap. No, I am not on Intel's payroll, but this substitute is a must have for every Mini 9 owner.