Here's a thought that occurred to me, while I was working my way through the corrections and editorial suggestions for the sequel to Stealing Light: who reads a sequel without reading the book it's a sequel to?
There's a certain degree of infodumping in the new book, designed by me as a kind of 'reminder' of what happened in the first. Most of it happens in the first chapter. Pan want me to be sure people know what's going on if they haven't read Stealing Light. But here's the thing ... maybe it's just me, but I can't imagine picking up the second, third or whatever book in a series without reading the first one. I therefore assumed that if anyone was picking this up, they'd be picking it up after having read Stealing Light.
So does this mean that lots of people out there will read a series of books in any old order? I'm not saying it's always a bad idea - I like George MacDonald Fraser's Flashman books, which have a chronological order, but you can pretty much jump in anywhere and have a pretty good idea what's going on. But I can think of quite a few series of books I really wouldn't want to read out of order.
The only time I remember doing so is Vernor Vinge's Marooned in Realtime, which turned out - I hadn't known this when I picked it up - to be a sequel to another book called The Peace War. I could read Marooned fine without having read The Peace War, but if I'd known I think I'd have hesitated.