I love this new feature - not only does it let you see who's visiting it let's you see what other blogs they're following besides yours - like I really need to add more blogs to my Google Reader but there you go. So, even if you're only visiting by chance, even if you visit and never comment please click on the Follow This Blog feature - it'll give me some new blogs to read!
You can find out more about it here:
Official Google Reader Blog: Get your Blogger following fix (in Reader)
Update: This is great! Whenever you follow a blog it automatically adds it to your google reader; I've already added at least 10 new blogs yesterday and today. Keep following!