I use at least 3 different ISP's depending on the site that I'm at, and at present, Ryanair was up on one of them, and is down on the other 2.
Speaking to tech support at the ISP here, they are telling me that the (strong) rumour on the web grapevine is that Ryanair are in the middle of a server migration, and it seems that the process has gone badly wrong, and that DNS addresses are getting badly confused and screwed up all over the place.
There's no indication from the Internet rumour mill as to how long this is likely to continue.