I'm experiencing the same issues, from about 7pm to about 11pm ( usually not up past that time to check!) my DSL is slow and I get dropped connections alot. I don't have wireless, so its not an issue of providing free internet to my neighbors. Its been happening for the past 6 - 8 months.
I've tried new drivers, power cycling the router, new cat5 cables, nothing has helped.
I'll be upgrading to FIOS once its available and hopefully this will stop happening. I live in the US, SE PA to be more exact, where are you at King?