Being a web developer, I am very interested in the fact that I can build websites within the Multi Theft Auto server. I was toying a bit with this yesterday, when I noticed that my FPS significantly dropped when I had this GUI open. Chaos then informed me that it isn't the GUI being open, but the cursor being on screen that causes the lag.
The item system, every time your screen renders a frame, loops through every single one of the 15,000 world items currently placed in the server if you have your cursor showing, in order to determine what item your cursor is hovering over, so it can show you the item name. I have yet to determine the reason for this, because the exact same effect can be achieved by using processLineOfSight.
Well, I guess at the end of the day, all that matters is we got those precious FPS back. Hopefully when the server returns, we'll have a slightly less buggy product to show off to you.