I have a Macbook Pro 2.33 Ghz 4GB RAM 667mhz ( only 3GB useable) It came with Tiger and i was very happy with its performance and boot time and also stability. When leopard came out i did a clean install and thought at first it booted a lot slower, apps took longer to load and ive had a lot of problems with it never sleeping properly and finding a roasting hot laptop shut in my laptop bag NOT GOOD! It was until i was playing around with 'Mainstage' that comes with Logic that id had enough. the cpu usage during mainstage was always about 25% even when doing nothing and it would often peak when i never remember there being any problem before. There was also a noticeable lag after pressing the key which i never had before. so, i reformatted, partitioned with 2 partitions and installed Tiger on one, leopard on the other. I installed the same programs on both partitions and so far i dont see me going back to Leopard! Firstly, it boots Tiger about 5 seconds faster. Apps load noticeably quicker. Mainstage doesn't lag and has NOT cpu spiked at all in Tiger. I havent had safari crash like it did in Leopard either and battery life seems to be improved by roughly 40 minutes and ive noticed the cpu or gfx fan is quieter as well. Now i also had (just sold) a Macbook 2.2 Ghz whch came with leopard but didnt really exibit the same problems ive had with my macbook pro. mainly mainstage did not spike or lag. Is leopard maybe just more optimised for newer macs hence why my older rev macbook pro prefers Tiger?