It's such a wonderful coincidence that we came across OctaGate SiteTimer today - a free online service that will tell you exactly how long it takes for a user to download one or more of your web site pages. Exactly what we wanted to improve the performance of our blogs.
You type the site URL and SiteTimer will download each and every element from the webpage including Images, Frames, Scripts and iFrames.
If your site has Youtube videos, advertising code inside iframes or external javascripts, you would know right away if they are making the site slow.
SiteTime service will prepare a complete report about every object found on the webpage including details like how much time did it took to download a particular graphic, what was the size of that graphic and if it did exist at all.
SiteTimer is a must bookmark for all bloggers and website owners. Site loading diagnosis has never been so simple.
OctaGate SiteTimer [Found via the Ajaxian Blog]
Bonus Tip: If the first part of your page loads fast, and the parts that aren't visible yet take longer, than that's ok, because the users don't care about information that they're not ready to look at yet.