Quite a few people experiencing this problem have been told by tech support that it's due to "congestion" and that a capacity/bandwidth upgrade expected to go live on 20/21 June will fix the problem.
Currently 4am ... highly doubt there are many users active ... and yet:
DNS error: http://i.imgur.com/ZQZ9rRT.jpg
Speedtest: http://www.speedtest.net/result/5391809004.png
Line stats: http://i.imgur.com/wWBnPCd.png
Hardly likely to be congestion at this time of night, yet the behaviour remains exactly the same as throughout the day and during peak periods - good line sync; good throughput (though varies with network load) but shocking connectivity due to DNS resolution errors.