When I receive reports that my website is running slowly, I would like to be able to point the end-users to a performance/profiling tool that is easy to use and that has a feature where the end-users' report can be sent to me. Can anyone recommend a site or browser plug-in like this?
In the WebKit Web Inspector, it appears you can save all data in HAR format. Then, a tool like this can display HAR data:
Net Export for Firebug looks like it may work for this problem.
It's not exactly a tool for end-users to use and report to you, although that approach may be problematic in and of itself because performance problems often have a way of disappearing as soon as you try to measure them.
If you need real application monitoring with end-user metrics, take a look at NewRelic RPM. It's not cheap (although they do have a free 'Lite' version), but it's the best application monitoring software I've used, and actually measures end-user response time and breaks down the request, response, and render times so you can locate bottlenecks. It also includes server monitoring and a host of metrics and reporting that will help you to do serious tuning and eliminate bottlenecks.
Even the free version is fairly useful, and you get a two-week free trial of 'Pro', so it might be worth taking a look.
Personally to test the website performance I use this Firefox PLugin - YSlow. It basically gives you more details what is the main problem. You can also install Firebug as a addon onto Firefox and check the NET tab and it will show what is taking so long to load.
Once you identify what is slowing your website try to remove it and see if you make any progress. If this file is required try to minify it or find a replacment.
Just a quick question... are you using the site in HTTPS/SSL ?