How to speed up my iMac (Mid 2007) running Lion I've had this 24" Al iMac since it came out in August 2007.


2.8 Ghz Intel Core 2 Duo (X7900 Core 2 Extreme)
2GB 667 DDR2


The machine has never been rebuilt, and the profile is the original profile from my original iBook G4 back in 2004 (migrated to a MacBook and then to the iMac)

I'm loath to spend any money on the machine since it is coming up to 5 years old, and I want to save up for a new one later this year.

I want to know what software tweaks that I can use to speed up the iMac as it is now slow for much of anything except the basics.

I'm looking for ways to speed up the boot time, runtime memory efficiency, and responsiveness.

Edit for clarification purposes:
If you have any quick fixes, they would score higher for me than say having to rebuild the system (sorry Stuffe)
If you don't want to spent money, then that rules out hardware upgrades, which means you are down to software.  You are already running the latest OS (and anecdotally at least for anything reasonably up to date the received wisdom is that you gain a speed boost with new OS releases from Apple on the same hardware) which means you are down to configuration.

So, as you say you have never performed a rebuild and you have potentially 9 years of cruft kicking around gathering dust I would simply test out your backup strategy by ensuring you have copies of everything you need, and perform a fresh install, recovering back only that which you are sure you need and still use.