Basically, Fiddler is an IE add-on that monitors what comes down the wire to the browser whenever you request a page. In includes all the details about what types of files are downloaded (jpg, swf, css, js etc) and how long it takes. It even provides a pie chart to show what file types are causing the biggest payload. My first test on the site was with all of my cache cleared (so that I measure the performance of the first time visitor to the site). Yes it was definitely slow. My second request was done without clearing the cache. In this report however, it showed that although the flash files were being cached, All of the images stored in the SiteCollectionImages library were not.
So Fiddler helped me to identify that the BlobCache had not been configured on the server. This is a setting in the Web.Config file. It helps IIS to store images that are stored in SharePoint (and therefore in the backend database) to the local file system. Thus making subsequent requests for those resources a whole lot quicker (because a SharePoint database request is not required). The syntax for BlobCache is as follows:
Pipeboost helped me to identify whether or not IIS Compression had been configured on the production server. As most of you would know, browsers such as IE can handle compression. There is a handshake that goes on between the server and the browser to see whether the browser supports compression. If it does, then IIS compresses the contents (thus reducing the payload) and sends it to the browser, where it is decompressed and displayed to the user. There are two types of content that can be compressed - Static (like images) and Dynamic (like ASPX pages). Static compressioncan compress the file as well as stores it in the Temporary Internet Files directory, so that it can be served up quicker next time. Dynamic waits for the ASPX to return its content, then it just sends that page compressed back to the browser (i.e. it doesn't store it in the Temporary Internet Files location).
There is a great article at http://www.dotnetjunkies.com/Article/16267D49-4C6E-4063-AB12-853761D31E66.dcik that explains how to setup IIS Compression. At the end of this article, it talks about Pipeboost, which can tell you whether or not the payload returned from the web server is compressed (i.e. via IIS Compression).