Overall, I’m incredibly impressed with their effort. The biggest draw is that your data is in real-time, and you actually own it all. Maturity-wise, it’s not quite to the level that GA is, but it’s moving fast, and given a year or two, will probably be toe to toe with GA, feature-wise.
If you’re not running an incredibly complicated campaign, Piwik is refreshing in it’s simplicity. Don’t expect the bells and whistles that come with more mature products, but what it does do, it does well.
For now, I’ll keep running both Piwik and GA. I have a feeling that Piwik is going to turn out really nice in the long run, but for now, GA is still clearly leading the pack.
Note: Piwik was at v0.9 at the time this was written