Before heading to graduate school, and feeling unsure of my preparation, I asked my undergrad professors what I could do to improve my chances for success there. One of them suggested I read two volumes of Putnam's Philosophical Papers. I dutifully did so, and when I arrived in graduate school I was thoroughly convinced I would never make an original contribution to philosophy--Putnam combines technical virtuosity with an astounding grip on the interconnected-ness of issues in lots of domains.
Much to my surprise, at Chicago the admiration for Putnam was not widely shared by the philosophers of physics and logicians. Where I saw virtuosity my new teachers saw argumentative holes that ought to slow down more careful thinkers.
When Putnam visited Chicago (ca 2001) I attended one of the seminars he co-taught (with James Conant). It was a course on skepticism slanted toward discussion of McDowell, then recent Putnam, Stanley Cavell, Michael Williams, Charles Travis, and Barry Stroud amongst a few others. Putnam was an enchanting figure who could get excited about an eclectic mix of arguments and positions. Philosophy felt alive in the presence of his restless mind. I found especially endearing his generous tendency to assume that students' questions were subtle and worth developing; I have never sounded so smart as in his interpretations of my remarks, which he would develop (pro or con) into extremely insightful argumentative permutations many layers (of moves, and counter-moves) deep; it would be very illuminating even dazzling, while simultaneously leaving the original question/problem still obscure. He could be disarmingly frank, too; when, during a conversation in his office, I asked him for his reasons for the turn away from Carnapian explication to his more Austin-ian projects, he said -- with obvious admiration for Carnap -- that explication was just very difficult. (Putnam tells a more subtle version of his story here, pp. 178-9.)
He was one of the gentlest and generous professionally successful philosophers I have met. But in looking back at my notes from the period, I also found him obsessed by his own past work and his stature as the last, and thereby simultaneous end, of analytic philosophy. (With the benefit of hindsight it's clear that at the time he had not fully grasped the significance of Lewis' work for the profession.) His attitude was odd because he was constantly finding new things to say about lots of stuff.
As an undergraduate I was introduced to his work on Skolem's apparent Paradox (“Models and Reality”) that generated a fierce response by Lewis (which I discovered much later); one of Putnam's gifts was to turn abstruse issues in philosophy of logic into questions of philosophy of language/semantics (and metaphysics). I was also taught "Meaning and Reference" (and introduced to twin Earth). I did not realize it at the time, but Putnam's views on/version of Quine and the analytic-synthetic discussion were also taught to me. (In fact, I have come to think that Putnam, who was a very effective PhD supervisor -- he trained a whose who of the profession [including my own supervisor and lots of other intellectual mentors]--, was more responsible for how people understood Quine than Quine himself in the 1970s and 80s.) Functionalism in the philosophy of mind, the brain in the vat response to the skeptic, and the indispensability argument on mathematical objects, were all part of my undergraduate bread and butter (and that's just the tip of the iceberg on his contributions to a vast array of projects in analytical philosophy, mathematics, pragmatism, epistemology, philosophy of science/mathematics, meta-ethics, and even Jewish philosophy.)
When I was asked to teach intro to philosophy of mind in Leiden about a decade ago, I remembered a remark of Dan Dennett's that Putnam's early papers from the early 1960s are head and shoulders above anything else in philosophy of mind of the period, so I used the opportunity to read them carefully and teach them as responses to Turing. Decades after they were published, they (including "Minds and Machines") still sparkled with intelligence connecting philosophy of mind, artificial intelligence/robots, and moral psychology (they also defied easy summary to my students); they prefigure lots of debates and issues made famous by lesser lights.
Lots of wonderful Putnam stories circulate that rightly emphasize his generosity. Unfortunately, I was present at a rather memorable and unpleasant author-meets-critics session at, I think, the central APA in which Putnam was one of the 'critics' of McDowell's Mind and World (somewhere in the 1990s). Putnam's comments were characteristically very generous, including acknowledgment that earlier he had underestimated the significance of McDowell's work. McDowell's response implied that Putnam had misunderstood his book. It was an unpleasant exchange because Putnam quite clearly and eagerly wanted to emphasize points of agreement, while McDowell was not having any of it.
I close on a lovelier note. The first time I 'met' Putnam 'in person' was at one of the New England undergraduate philosophy conferences at Tufts. Before he started his keynote, he made a pitch to one of our graduate students to enroll at Harvard. It could have been an awkward moment, but he made it seem that her presence would inspire the department (which all of us knew also included Rawls, Quine, Nozick, etc.), and, along the way, made all of us feel that we could contribute to a shared philosophical endeavor. He will be greatly missed.