How often do you crop up on the web? How many times do your books crop up? Unless you search for yourself on Google every day - and if you do that, it's time to get a life - you probably don't know. Google Alerts can do the checking for you. Register, enter the term you want to search for - your name, the title of one of your books, the name of your main character - and pick 'comprehensive' as the search method and Google will email you each time your chosen phrase is found in new pages going online.
How useful it is depends on your name/book title. If you're called Gordon Brown, you might as well forget it, as wading through all the references to Gordon Brown to find one that relates to you, the real Gordon Brown, will take up so much of your time you won't be a writer any more.
Why do this? Vanity? 'Oooh, look at me, look at me, I'm on Google'? No, though you could do it for that reason. It's a good way of keeping track of reviews of your books and, increasingly, pirated uploads. That is, electronic copies of your books posted without your permission (or your publisher's) permission, usually for people to download for free. You can then decide whether to issue a DCMA take-down notice (more on that another day) or just glory in how popular your book is when it's free. Either way, it's good to know. Knowledge is power. And knowledge is also smug-juice.