If you do not need 3-D graphics on your laptop or PC, (and really, who does?) and you desire to improve the performance of these systems, then you would do well to disable Aero right out of the box. This assumes that you have the Ultimate or Business editions and the hardware to support Aero, but as Aero is really just a hyper colorful desktop, you have to ask: do I really need this? In most cases, the answer is no. Aero DOES look good on my Dell OptiPlex 3100 at work when I have it on (usually to demonstrate how unimportant it is to a curious customer) ... For example, I can in fact have Aero turned on, and it does not affect performance too much. But that is because I am very stingy when it comes to desktop real estate and I obsessively close windows throughout the day. I cannot stand to have more than 10 windows AND/OR applications open at once. That pretty much leaves me with a few remote desktop or VNC sessions, a few Outlook 2007 related windows, maybe a 'MYSql' query browser or a couple of Excel spreadsheets, and of course one or two Internet Explorer windows. That's right: two.
But that's just me.
Most people I work with and those I support tend to have 10 windows or applications open within 2 minutes of work. They are well past the 25 mark by noon. For these folks, Aero should be turned off. Graphics related bells and whistles NEVER improve perfomance on a PC or laptop, so why enable it? Unless of course, you keep your applications to a minimum.