rlange - 2:06 pm on Feb 20, 2012 (gmt 0)
What do members think of this idea?
Is this an attempt to clean up those 404s or an emotional lashing out at Google?
If it's the former—and someone else with more experience than me can confirm or deny this—blocking Googlebot will pretty much guarantee that those 410s won't be seen.
If it's the latter, I don't see how blocking Googlebot in robots.txt can be beneficial in any way other than to offer emotional closure on a broken relationship (like throwing out everything that reminds you of your ex-girlfriend).
If you're giving up on Google, there's no reason you can't leave your site open to Googlebot, focus on Bing/Yahoo! and just take whatever traffic Google sends your way.