Similar problem here... Running on a Wi-fi connection with a ASUS WL-530G router with a disabled firewall. Tried manually setting the DNS servers to the google public dns servers ( 8.8.8.8 and 8.8.4.4) nothing happens ...
When run apt-get update through terminal all goes smooth and finishes but it goes REALLY slowly... same goes for pinging the repository site of maemo.. looses first 12-13 packets and then goes smoothly :O Though it seems the problem only occurs on my home wi-fi connection since I tried it briefly in a cafe and it didn't seem to have any trouble updating :/
The connection isn't slow,signal is perfect at home and there is no such problem when i ping the repository site through my PC which is connected over cable to the same router :S

Strange thing is that it sometimes manages to update itself >.<

Any help will be appreciated