is it speedy to include stylesheets/images from another domain?

[unwashed potato!]

so i've got 5 different websites that all use the same custom built theme. 1 is designed to list all services, then the other 4 are sites dedicated to each service. sometimes on those sites images are say used for deals on site 1,2 and 4, or 1 and 4 etc.

at the moment i've been uploading the images to each domain even though the domains are all on the same server. is it ok in terms of speed to upload the image to the main domain and then have the others link to that image on the main domain?

same with style sheets? can i have one master style sheet on maindomain.com which all the others link to?

if so, is there a quicker way to link to the image/stylesheet other than pointing to the exact path of the file?

 

[touch]

There could be a slight overhead as it may need to do an additional dns lookup for stuff on another domain. The actual transfer time would be the same though.

If people are likely to be browsing all of your sites at the same time then it would have the benefit of being able to cache these resources.