There are only so many names in the world, and all of them have been used by somebody, somewhere. There will always be somebody to point out that so-and-so has the same name. I don't worry about it. I let characters pick names that fit them, and if the story is good, the character real, the name will become as invisible as 'said'.
I once new a police officer with a very long, very complicated last name with lots of z's and c's and w's in it. I overheard him discussing it, and he said he'd never seen that name anywhere outside of his family. He spelled it for them, and that clicked for me. I had just read a book with a character who had that same last name. I had to bring it in to show him.
What irritates me is characters with very long names that are never shortened. Evangeline. Emmalique. Samantha. Dominique. I want to say it quick and move on. Gimme Kat, Sam, John, and Carl any day and let me enjoy the story. I've got a Katrina in a WIP, shortened to Kat, and I don't care how many other Kats are out there: My job is to make my Kat and her story so unique and interesting that readers will remember her for that- not vaguely recall a humdrum story that had a character with this really different name.
Now having too many characters with names that are similar- that bugs me. I do it. I do it and I don't catch that I do it until long after I've done it. Right now I have a WIP with two male characters; Dean and Dave. Can't change Dean because his full name is Dean Dean Dean. Says his momma named him that to save her time when she was pissed at him. Dave is the title of my story and I'm going to have to be really persuaded to change it. But he's dead- sort of- so it's not like he has a lot of dialog.
The female character has five dogs, and all of them have names that start with M. I did that on purpose because that's her personality, and they're different enough- I hope- not to cause too much confusion. They're dogs. Not a lot of dialog tags there, either. Meg, Molly, Max, Mose, and Marg. At least they're all different breeds, so I can refer to them by that.
But yes, at the risk of sounding hypocritical, I do hate it when a bunch of characters have similar names. Even had an editor call me on it once, insist I change one of them. Guess I'm going to have to stop trolling the phone book for ideas.
What I'm curious to see now is, how many Baracks start to crop up in fiction.