I did a little digging into Radio Userland's RSS Rankings report today to figure out what the numbers mean. The count is the number of times a Radio Userland user checked your RSS feed and found one or more new items. If you have five subscribers and you send 10 items during the day, your daily count could be as high as 50, though it's likely to be lower. Some subscribers might not be online to receive all of the items that day, so they only show up when they're actually receiving items from your feed. Some subscribers might only check your feed once and get all five items, which increases your count by 1. And so on.
Stats are compiled for every RSS feed in someone's Radio Userland news aggregator, though users can turn this reporting off to keep their own feed-reading habits private. To find out who is keeping up with your feed in Radio Userland, use this kind of link:
Replace Your%20Weblog%20Title with the name of your weblog as specified by the TITLE tag of your RSS feed, replacing all spaces with %20, the URL escape code for spaces.