"Have Space Suit, Will Travel" is the first Heinlein book I did-and-didn't read.
Wait, let me explain...
Like you, I stumbled across it in the school library as a kid, in a fat large-type hardback edition. I started reading it, but didn't really get "into" it because it was just a kid tinkering in his garage on an old suit and stuff, and thus I hadn't gotten too far into it when the book was due to be returned.
*Years* later, when I was eighteen, my girlfriend at the time introduced me to what I thought was my "first" Heinlein book, "Stranger in a Strange Land". Like all of Heinlein's books, it had more mind-stretching ideas than a stack of most lesser works, so I began devouring all his books (I've now read every one of them, and own copies of most).
The last books of his I read were his so-called "juvenile" books (all still imminently readable for adults), and thus I came full circle -- one of the last ones I caught up on was "Have Spacesuit, Will Travel", and as I read the first few chapters it came flooding back to me that I had checked out and read this book *many* years ago as a young child.
The really funny part is that I remembered exactly where I had stopped out of youthful boredom -- it was HALF A PAGE before an alien space ship comes flying out of the sky and grabs the main character from his back yard and all hell breaks loose... (He was already standing in his backyard dressed in the spacesuit at the point I stopped reading.)
If I had read just one more page back when I was a kid, I'd have gotten to "the good parts", and read the rest of the book. Who knows how much sooner I'd have caught up on Heinlein's books at a much younger age, and what effect that might have had on my formative years.
Oh well, better late than never I suppose.
Wow, I just noticed how old the posts are to which I'm responding, LOL! Who resurrected this dusty old thread? ;-)