Now, as a grown-up, every time I look at it I wonder. It's perfect, but not logically so: if there are windy willows anywhere in the text I don't remember them, so you're relying on the phrase itself and what it might evoke. Which may perhaps be that whole nostalgia piper-at-the-gates-of-dawn aethereal kick - even before you read the book, it might be - but that's only the shorter side of what the book's about. Which I guess is why the play is called Toad of Toad Hall.
Anyway. There it is; I think it's interesting. Like The Long Grass Whispers, which is another of those title/names I never thought about until I was a grown-up. (Does anybody still read The Long Grass Whispers? I was devoted to it, but I never saw it on any other kid's shelf; and then I didn't think about it through the years of my adolescence; and then when I was a young man I saw it in a children's bookshop and got excited/reminded, but didn't buy it, and I've never seen it since. Wikipedia's never heard of it, but Google remembers...)
Also, I have been reading Steven Brust with my morning coffee, and I just got to the bit where Sethra Lavode's servant turns out to be called Chaz. This took me aback, in a gratifying kind of way. Independent Chazerie! (Taltos is copyright 1988, so it doesn't exactly predate me, but it's coeval with my first book with my own name on the cover, so I think we can safely say he didn't get the name from me.)
Which reminds me: now that I have a Kindle and am inclined to read onscreen fictions, there's something else out there with a Chaz in it, that I need to investigate... *exit, in pursuit of Shadow Unit*