blogspot.com. There is no known workaround at this time.
Update, Thursday, 9:45AM: We’ve received word that this problem is at last fixed. For reals this time.
Update, Wednesday, 6PM: Reports continue to come in that this is not fixed for all cases. Our engineers are in contact with at least some of the ISPs and are working towards a solution. If you are experiencing this problem, please contact your ISP and also contribute to this thread on the Blogger Help Google Group and let us know who your ISP is. This information will help us fix this once and for all.
Update, Tuesday 10AM: This has been sorted out and fixed.
Update, Monday, 9:30AM: We’re hearing further reports that this problem is not solved, and there are indications that there is a misconfiguration in the affected ISPs’ routes. We appreciate your patience as we work with them to get this fixed for good.
Update, Sunday 4:25PM: We’ve instituted our own network workaround for this issue, which should resolve the problem for affected users. We’re following up with the ISPs to diagnose the root problem.