Not that much.
I have all the Star Trek Voyager books covering seasons 1-3 and I found no problems to sort them into a timeline without having too many errors and contradictions which disturbs it.
There are some small contradictions here and there but when I come to one of those I just shove it aside mentally and continue to read.
(For those who like the Voyager seasons 1-3 books and wonder where the odd things and contradictions are, read my comments about them in my book reviews)
As for books from other series, I've read some of them occasionally and have no problems with contradictions there either.