I have been doing it by checking the author's pages on amazon, but I forgot to check some of my favorite authors. I tried google alerts, but I got too much info so it wasn't particularly useful.
It seems like the stores/publishers/authors would want something like this out there too. I would say it might not affect people who don't read that many authors, but one of the books I missed was in a series I am very addicted too (write faster JD Robb!).
It doesn't sound technically hard to do, I think the problem would be gathering the data itself. I could see store specific versions, though a generic version would be more useful. I snagged the sony store software and am trying to see what it offers in this area. It wouldn't be perfect as they don't have all the same books as amazon, but it would be better than nothing.
Someone should write an android/iphone app or get GoodReads or Calibre to add the feature.