What is it that actually causes a computer to slow down?

There are many causes that happen over time. It's hard to pinpoint one exact problem.

 

Applications that auto-start are a major factor. The more resources the system needs to load, the longer it takes.

 

I've had my MBP for 1 1/2 years. It hasn't slowed down at all.

FWIW, all the apps I use constantly I have set to open at startup. That way I don't have to wait when I use them, Firefox, OO, and Parallels in particular.

 

I think it's less that your Mac has slowed down, and more that you realize how much slower it is in relation to newer models. It's a perception thing.

Either that or its gremlins.

 

all my money is on the gremlins

 

yep. gotta be those gremlins

 

Try running the Maintenance scripts. You can use the MaintenanceWidget if you like. In addition, if you have any kernel extensions installed or login items, boot time will go up quickly.

 

How much RAM is in the old Mac compared to the new one? Newer ones tend to have more RAM which is a big factor. How fast is the old hard drive? My iBook has a 4000RPM, newer Macs have 5400RPM or possibly 7200RPM. Newer processors have more L2 cache on the chip, means the processor can access common instructions faster.

 

Nah, sunspots, definitely sunspots.