If anyone here has any thoughts on something else to tune or play with, let me know. Overall, the experience of buying an Ad on Facebook was far better than my very limited experience with Adsense.
1) I think your target demographic, looking by the # of impressions. Try to go a little bit broader than just "tumblog". Try "tumblr", "blogging", "rss", .etc to reach a bigger audience
2) Your CPC is way too high. With FB it's best to go below their suggested bid, and gradually up your CPC amount until you start getting the desired impressions.
3) I'd gather a lot more data before making any kind of analysis on the data you're gathering.
4) Your CTR looks to be on the right track, although still probably not enough data to tell if it's stable yet. 0.1% is alright for a display ad on a social networking site. I'd still try split testing a couple different versions of your ad to see if you can up that. You always want to be split testing, constantly cutting the weaker performing ads, and making a variations of the better performing ads.
Another tack, since it's a personal blog, is to target people based on similarities to you, rather than interests. "Founder" as a keyword targets 22,000 people in the U.S. "Robotics" targets 13,700. "Startups" + "startup" targets 4,700. If you add age-targeting on top of this, I bet your conversion rate from click-through to follow / RSS subscription would rise.
For example, I could have "sign in" for accounts, using twitter or facebook connect. Then the "tweet this" link could be push-button, not the links to http://twitter.com/home?status=some_manual_posting_bs
RSS subscriptions that can also power email newsletters are certainly in the mix.
What text would you suggest? Obviously the title of the blog is pretty bad for the intent here.