The mainstream mass-market review requests are starting to pick up...
My primary source of books to review has been (and probably always will be) the technical publishing firms... O'Reilly, Apress, Pearson/Prentice Hall/Addison-Wesley, and others. Most of my recreational reading is provided courtesy of the library that's a block away. Occasionally the odd request will come in via email from a non-tech author asking if I'd like to read and review their book. It's a nice break, and it usually gets me to focus on a book that I might otherwise not notice.
As of late, I've been attracting more attention from the mass-market publishing houses as well as from authors who I consider more well-known. Simon-Schuster just sent me an advance copy of Matthew Reilly's latest cliff-hanger adventure, and Harper-Collins has a FirstLook program that has provided some advance copies that have been very well done. And today, I got an email from Joseph Finder, author of Company Man, asking if I'd like to get an advance copy of his newest one before it comes out in May. And it still blows me away when I get an email from a big-name author who found my review online and wrote to say thanks.
Nothing like having your drugs of choice delivered to you for free... :)