One problem with comparing your work to the work of another author comes when your potential reader HATES the author you just compared yourself to. I mean, everything else could be going along just fine, and they're halfway to one-clicking, then BAM, you've compared yourself to the dreaded author. Lost sale.
Which, I guess would be okay because, if your book is really like that other author then you don't want her detractors reading your book and giving you loads of bad reviews. On the other hand, if your book really isn't that much like BIG NAME AUTHOR's work, then by saying your story is like theirs, you've just screwed yourself out of a sale. Or left her fans feeling let down.
I try not to compare my work to other writers' books. Aside from the above, I have a tough time comparing authors. Those 'compare and contrast' assignments in high school? Yep, bombed them. Every rare once in a while, I'll be reading a book and think to myself 'this is kind of like...' but it's not often. And who knows if the way I'm seeing it is the way other people will see it? Know what I mean?
Anyway, it's a slippery slope. I'd avoid it unless you're really really sure. Like, say, if other people have told you 'this reads like a Michael Crichton novel' or 'hey, this story could've been written by Terry Pratchett', it might be worth something. Awesome praise, but I'm still not sure I'd use it as a sales tool. Not that I wouldn't want Crichton or Pratchett's reader base, but I also don't want that reader base to be disappointed.
Better off to just be you. And hope the readership loves you for the way you write.