pitch class set analysis

just began studying it...what's your view on it as an analytical and compositional tool for atonal music...looking over Schoenberg's op. 11 myself right now, but I wonder how often sets were used deliberately rather than coincidentally...recommend any pieces for set study?

Theories and analytical techniques aren't created until after the fact.

Isn't op. 11 the Chamber Symphony? That piece is pretty much of the late German romantic school, he even uses key signatures!

no, the chamber symphony is op. 9...the 3 piano pieces are 11

Read Allen Forte's analysis of Stravinsky's Rite of Spring. Some composers (Webern, Varese) are more amenable to this type of analysis more than others. In Webern's case it is an outgrowth of 12-tone theory and was pre-planned. In Varese's case it is more that he heard his music in terms of set structures.
With all twelve tone music it is the basis of the theory so it is more interesting to study those early atonalists like Scriabin. Ives would be an obvious choice but I have never seen any of these type of analyses of his music.