Over the last few weeks I've been making several changes to http.debian.net to detect mirrors that don't follow Debian's mirroring guidelines and end up causing problems to the end users. The changes will mean less hash mismatches and similar errors.
As I wrote back in December, the redirector is becoming nicer but also stricter. Some of the changes I recently made caused over 30 mirrors to be completely disabled from the redirector. This is not ideal and I don't like having to disable mirrors. They are contributions afterall.
The only thing I can do, and can't stress enough, is encourage people to use an up to date ftpsync script (available at project/ftpsync/ on every mirror) to mirror Debian.
It takes care for you of all the little but important things needed. Really. A mirror that uses ftpsync is easier for the administrator to properly configure, and provides a consistent mirror for the benefit of the users.
Speaking of ftpsync, there is a new version! If you use ftpsync please upgrade it as soon as possible.
Other improvements are on their way. Contributions are welcome (if you like refactoring, there's quite a bit of explicitly-redundant code in check.pl that should now give a better idea of the way it needs to be refactored.)