It depends.
First, it depends on whether the book is intended purely as a puzzle, a work of suspense, a thriller–or whether it is meant to function as a novel. If the latter, then personal life details belong and improve the book. Case in point: Lawrence Block’s Matt Scudder books. Scudder’s personal life is an important addition to the books. The details about his relationship with his wife, connections with his kids, etc., help to round him out and provide extra understanding of what he’s doing and what’s motivating him to do it. It helps that Block is a very fine writer, and he can pull this off quite well.
Another example: the Anna Pigeon series by Nevada Barr. While I haven’t liked some of her latest books all that much, she’s another terrific writer who is able to make Anna a more interesting, if not always more sympathetic, character by virtue of sharing (some) aspects of her personal life. That in turn adds to the reader’s enjoyment of the book. (Well, mine, anyway.)
And even when the characters are a bit more cardboard and the puzzle is more at the forefront, mysteries can be improved by some (emphasis on some) personal stuff. I’m thinking of books like the Deborah Knott series by Margaret Maron, in which part of the point is keeping up with Deborah’s enormous family. Now, I think sometimes–okay, often–it goes too far, and I find myself skimming past long descriptions of who’s related to who and how and Deborah’s latest discussion about home furnishings with her husband, grousing “Let’s get back to the action”; still, it’s part of the charm.
But there are some examples of authors who can’t carry it off. In general, I think it’s because the authors think their characters are more interesting than they actually are, or don’t have the skills to bring them to life. Or both. Prime example would be Marcia Muller. I gave up reading her Sharon McCone books in large part because the good parts of the books–the puzzle parts–were increasingly being dwarfed by McCone’s personal life, which was neither interesting nor illuminating. William Tapply’s books about Brady Coyne had the same problem. I’d say Patricia Cornwell would be another example, but of course she seems to have become certifiably insane over the last 15 years, so there’s that…
Bottom line: Yes, when done well and in a book that can benefit from it; no, otherwise.