It has been almost four months since we released Piwik 3. The major new release came with a new UI, performance and security improvements. If you are still on Piwik 2, the security improvements alone should be worth updating your Piwik now to Piwik 3. We cannot recommend this enough.
Since the Piwik 3.0 release we have released three new versions that fix over 250 issues including more performance and security issues. And new features: the Life Time Revenue, or the Cross Domain linking feature to track visitors across different domains accurately. Also, most plugins from the Piwik Marketplace are now compatible with Piwik 3 so there is no reason to wait anymore.
The update to Piwik 3 should be smooth, but may take a while depending on the amount of data you have. If you have any problem with the update, feel free to get in touch with us. At Piwik and at InnoCraft, the company of the makers of Piwik, we have successfully updated many Piwik installations.