Google Webmaster Tools is one account you can't go without on Google. It gives you so much information and enables you to tweak your sites in so many aspects that I can hardly fit all of them into a single post. Along with many of its present features - showing other sites linking to you, popular searches, sitemap submission, geographical targeting, etc., Google have recently introduced a new feature.
Site Performance is the last menu item which will appear under the "Labs" section in your Webmaster Tools account. There you can find valuable information, also available if you use a tool such as YSlow (from Yahoo) and/or Page Speed (by Google). You can learn how your pages are performing in terms of loading times. You will get a very rough comparison with the rest of the web and most valuable of all - a historical graph of your site's performance based on the loading times of each page. A graph like the one below. Under "Performance overview" you might want to see something a little bit more different to the excerpt below, but you will at least have a good start to fixing the problem.
On average, pages in your site take 4.4 seconds to load (updated on Dec 31, 2009). This is slower than 68% of sites. The chart below shows how your site's average page load time has changed over the last few months. For your reference, it also shows the 20th percentile value across all sites, separating slow and fast load times.
In addition, you can follow suggestions on how to improve loading times on several pages. You will not get all your problematic web pages listed, but having in mind they most certainly suffer from one problem, you will be able to fix all of them according to the few examples given.
You will become aware of the problem, but as good as the service is at its current state, you won't be able to pinpoint important locations where your pages load slower than average. Luckily, WebSitePulse.com can help you out here. We will provide you with detailed information of not only loading times, but also response times for specific locations. Detailed logs, updated as often as every 5 minutes are also at your fingertips, depending on the level of service you will require. Sing up for a free trial with absolutely no stings attached. We hope you enjoy our service and benefit from it!