I delegated 10k, and was getting about 7 SBD per day, which worked out to around 22% annually; I did a post about it a few days ago: https://steemit.com/life/@libertyteeth/delegating-to-minnowbooster-progress-so-far-after-four-days

Just after that it went down to 1.7, then 2.7, then 4.7, 5.5, and yesterday 4.9. You can see my payouts by looking at my wallet -- I really like how everything is transparent on here. That stupid commercial, "what's in your wallet?" has an easy answer here. :)