When I talk about Islandia I am definitely thinking of the book that I remember reading on the 1066 and all that principle of history is what you remember, I do not for one moment think that re-reading it wouldn't disappoint, indeed I am pretty sure that I didn't actually read it all the way through the first time.
Essentially it is a utopia / travelogue - the hero is a young, idealistic American consul to Islandia a remote and isolationist island somewhere in the southern hemisphere. Much 'tell me professor' ensues, mostly via the French consul who has some sort of French text-book name like Monsieur Dubois. OK, cheated and looked it up, Jean Perrier!
The most obvious thematic similarity with Anathem is the interminable and somewhat tangential struggle across the North Pole in Anathem which echoes Islandia's hero John Lang's struggle across some snowy mountains - see also The Left Hand Of Darkness. Le Guin, of course, mentions Islandia in the essay / talk / thing SF and Mrs. Brown and it is weird how much of a debt The Dispossessed and The Left Hand Of Darkness seem to owe to Islandia. Obviously, The Dispossessed is more explicitly anarcho-syndicalist and TLHOD has the Gethenites gender changing.
My main recollection of Islandia is that it weirdly foregrounds the contraceptive arrangements of the female characters, and of course the term Tanrydoon (soil-place-custom), the subject of a world-class tell me ambassador infodump.
Anyway, I remember why this came into my mind in the first place, I was thinking of the odd dream I had in which I was going to get a train back to where I grew up and get my Dad to put the key under the doormat and it gradually dawned on me, first that he didn't live in that house any more and second that he is dead. Indeed, I think I had a phone conversation with him in the dream in which he reminded me that he is dead. But then, I have had dreams where I have had to remind him, so I suppose it all evens out.