I am currently running a number Piwik 1.6 install for medium-sized web sites. I am happy with the current performance and feature set, and am not inclined to update.
Is it safe to stay on 1.6? Will there be security patches for this version if exploits emerge, or is it advised to update to the latest version? What are the long-term implications (aside from security issues) of staying on 1.6?