Dynamically loading (AJAX) page content & performance/memory usage

is there any memory of performance issues i need to be aware of when i constantly load/append page content with AJAX like twitter/tumblr

i am guessing that as more and more content is loaded (when the user scrolls down), it will clog up the browser cache? is there a need for me to remove the older content (starting of the page). or will it be not required as it takes up too little memory, unlikely to cause a problem. if i remove the starting content, if the user 开发者_如何学运维scrolls up i must handle it?

I don't think you need to worry about this unless you're loading thousands of images. The only problem with constantly appending to the page is that the scrollbar becomes useless.