SInce migrating to plus.net last month I've had problems loading some common sites, like hotmail, amazon. From reading these forum pages, it appears I'm not alone. Manually setting the DNS server settings in my router, as recommended in some posts, failed to help.
However, my router company (ADSLnation) suggested changing the MTU packet size setting from the default 1500 to the (apparently British standard) 1458. So far (and I only did it 12 hours ago) so good. All those sites load as they should.
www.adslnation.com has more info about how to change MTU settings for Macs and Windows under its Support> Knowledge Base section.