One of the topics that fascinates me is how to provide subtle kinds of useful information to users of software. I like sparklines, typography, and subtle graphic design elements that call attention to information with the right weight.

One simple example I ran across today was the metric provided by StackOverflow on my profile for the number of days I’ve visited — 195 days out of just over a year since breaking down and creating my account.

So that’s just about right considering how frequently good questions and answers from StackOverflow show up in my Google searches. You can tell I don’t contribute a lot, and I don’t show up even every other day, but it’s not far off from that. That kind of information was surprising, since I never really thought about how many times I had come to the site.

What about your site or web app, or even iPhone app? Do you have quarter-over-quarter user retention goals? Do you think that your users would suddenly realize the value they implicitly already placed on your service if they saw out of the corner of their eye how much they used it? I had that feeling. If they saw how much they cared about it in hard data, would they respond more frequently to your requests to refer their friends to you?

Think about it. You might be able to tap into more power than you think with simple, subtle cues.