By default, FeedBurner already enabled the reach metrics for everyone. "Reach is the total number of people who have taken action — viewed or clicked — on the content in your feed. Subscribers is a measure of how many people are subscribed to your feed. At any given time, you can expect that a certain percentage of this subscriber base is actively engaging with your content and this "Reach" measurement provides this additional insight."
And other good news: FeedBurner MyBrand, the service that lets you serve your feeds from your domain, is now free. It used to cost $3-$14/month, depending on the number of feeds from your account. "With MyBrand, publishers can continue to take advantage of all of FeedBurner's services, but provide a transparent experience by running everything through their domain."
{ Thank you, Carlos. }
Update: FeedBurned confirms this. "Beginning today, two of FeedBurner's previously for-pay services, TotalStats and MyBrand, will be free. Not in the sense of soaring high above the clouds or recently sprung from the hoosegow, but free like you'll no longer gladly be billed on Tuesday for a burned feed today. We suspect this will be welcome news to the 450,000+ of you using many of our other free services, but understanding that your feed is your feed, you will need to activate these newly freed-up services in order to partake in their awesomeness."