No, I haven’t.
I do have some books which have been autographed by the author—some I won in online giveaways, some I was given or sent as a thank you for editing the books, and some I have purchased from the author at writing conferences. But none I bought at an in-store book signing.
Why have never attended an in-store book signing? This is mostly because I’ve (almost) never been in the same town as a favourite author when they’ve held a book signing.
Almost? There was one time … I was in Brisbane to attend the Omega Writers Conference, and one of the authors (Jo-Anne Berthlesen, I think) was holding a book signing that morning in the local Koorong store. Well, I had a map, but after completely missing the correct motorway exit twice, I gave up and headed for the conference venue. So I missed my chance to attend an in-store book signing.