I have tested this over 5 hours now and I can see that there is a performance issue somewhere. Installing the plugin is ok and gives me the exact same loading time. The problem occurs when I create a form with about 10 text entries, including email response. After that the whole page is about 0,4-0,5 seconds slower.
After deactivating the plugin it is still slower. The only solutions is to use a backup of the wp_options table. After that the site is back to normal speed.
Do you have any custom code or a plugin in place that changes how often WordPress checks for plugin update availability? Automatic update checks can slowdown WordPress as it has to check our servers for updates.
As for slowing down your site even after you deactivate the plugin? I've never seen that. It sounds like you may have something else going on with your site because it shouldn't be slowing down your WordPress install even when deactivated.
Nobody else is reporting an issue such as this and we have thousands of users, as you can tell from browsing the blog there isn't a widespread issue of the plugin causing their admins not to work. So there is something specific with your WordPress install that is going on. When deactivated, the code doesn't run so it shouldn't have any impact on your site.
