I regularly see gstatic.com in the status bar, what is that domain?
Google has off-loaded static content (JavaScript code, images and CSS) to a different domain name in an effort to reduce bandwidth usage and increase network performance for the end user.
increases performance by increasing, in theory, the number of connections the browser can use, by default, most browsers will only make two connections to a single server. While this is configurable, most users don't bother, so having content come from multiple domains, it can open two connections for every domain the site uses. This loads the content into the users browser faster.
decreases bandwidth by disabling cookies and other HTTP headers for the
gstatic.comdomain. Believe it or not, disabling headers greatly reduces bandwidth usage, especially if a page uses a lot of static files.static content can be offloaded to geographically diverse CDN servers. Google can push all the content to servers that are nearest to you. This is probably more applicable to a normal corporate site, as Google does a great job of pushing everything to a datacenter closest to you. But for a normal company, you could split out your dynamic content and your static content and then pay a CDN provider to host your static content, reducing your corporate datacenter's bandwidth usage, while improving load times for your user.
gstatic.com is a cookieless domain to deliver static content for Google. See this article for more:
Best Practices for Speeding Up Your Web Site - Use Cookie-free Domains for Components
When the browser makes a request for a static image and sends cookies together with the request, the server doesn't have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.
If your domain is www.example.org, you can host your static components on static.example.org. However, if you've already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.
Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the www subdomain and write the cookies to that subdomain.
If you're like me, you probably notice the gstatic domain because your browser is paused waiting for a resource.
If the domain you're seeing is
csi.gstatic.com
then note that this is NOT a static resource. It's some kind of internal logging (much like Google Analytics). If you do a Google search for csi gstatic you'll see that many people wait up to 30 seconds for this URI to be processed by Google.
Google, for their part, has never (to my knowledge) publicly mentioned csi.gstatic.com/csi.