I read in bursts really I can go weeks/months without then go through 6 or 7 books in a week. I've always been a very fast reader and if something interests me enough to give it a look I tend to read the entire series at once.
I think the biggest factor for me is if it grabs my interest or not quickly if something doesn't I don't try and force it just wait for the next thing that might.
I've an old Sony Walkman in a drawer that's is barely larger than the cassettes itself, my guess today there probably isn't money in them anymore so it's probably only a handful of company's making them and doing it as cheap as possible.