If you're a big Flickr user, chances are the recent comments URL is your new inbox. All my friends punch it up like a skinner box. The opposite URL for tracking the comments you've left on others' photos works in a similar way and is just as addictive. Obviously, after loading both for the tenth time today, I thought why don't I have two similar URLs for tracking the same info about my blog?
Emulating the first is easy -- most any blog software can give you a view of recent activity, which you can use to find out who is commenting on your posts and what is being said on your site. The second feature is a bit harder.
I know I'm not the first to request this, but I'd love to see someone propose a system that could track your comments across all blogs automatically. I think trackback pings could still do it if someone piggybacked a server onto TypeKey or something similar, so that every time I left a TypeKey logged-in comment, an automatic ping would go from a blog I was commenting on to my profile's personal trackback URL. I could then use those pings to create a page that looks like this, but for all (MT at the least, but hopefully other systems could play) blogs I read and comment on.
Lazyweb, don't fail me now.