There are not many CPs that interest me, but I placed a bid on this item in 2013. It is the 1910 Encyclopedia Britannica 11th edition set. This particular set is highly revered more than any other EB set. This is what the people in the early 20th century used as their "Google".
Here is an article from The Guardian about this set.
Older reviews found on Wikipedia:
Robert Collison, in Encyclopaedias: Their History Throughout The Ages (1966), wrote of the eleventh edition that it "was probably the finest edition of the Britannica ever issued, and it ranks with the Enciclopedia Italianaand the Espasa as one of the three greatest encyclopaedias. It was the last edition to be produced almost in its entirety in Britain, and its position in time as a summary of the world's knowledge just before the outbreak of World War I is particularly valuable."
Sir Kenneth Clark, in Another Part of the Wood (1974), wrote of the eleventh edition, "One leaps from one subject to another, fascinated as much by the play of mind and the idiosyncrasies of their authors as by the facts and dates. It must be the last encyclopaedia in the tradition of Diderot which assumes that information can be made memorable only when it is slightly coloured by prejudice. When T. S. Eliot wrote 'Soul curled up on the window seat reading the Encyclopædia Britannica,' he was certainly thinking of the eleventh edition." (Clark refers to Eliot's 1929 poem "Animula".) It was one of Jorge Luis Borges's favorite works, and was a source of information and enjoyment for his entire working life.
The CP needs more bids!