Yep - I've noticed a slowdown too. I was with BY.
Having looked into it a little, it seems that there have been routing changes within the BY & NTL networks as they attempt to merge them.
Ex BY customers now 'can' take a few extra hops through some NTL routers to actually get out on to the Internet.
I have also heard that the VM bandwidth to the US is less than the aggregate bandwidth available to NTL and BY customers. They may have reduced bandwidth to Europe too.