My two cents:
I'm in the process of finishing up my first novel. I plan to do three rigorous edits on the book -- once, reading through on the computer screen and editing as I go. Twice, reading through on a paper print out with a highlighter and fixing after I finish the reading. Third time, reading out loud from a paper copy with a highlighter handy.
Then I'll be sending out to a few hand-selected beta readers, gods bless their souls. And I'll fix anything THEY find.
Tedious? Yes. Time-consuming? Yes. Cheaper than some of the professional editing quotes out there that are more often than not lacking in any references or guarantees? Yep. Worth it? I think so.
Will every single error be caught? Probably not. But I think 99.99% of them will be. I hope, anyway. We'll see.