im using cs4, final cut and a bunch of others, some work fine but my font browser for instance doesn't work anymore.
Ralf go in to: applications> utilities > disk utility. open that and and select your base hard drive click the verify permissions button and if you need it, the repair permissions. you'll see another set of buttons for the Disk. Do the verify and then the repair. you can just click repair but im not sure if it will show you as much diagnostic info vs clicking verify first.
Basically this is similar to defragmenting a hard drive in windows.
On 10.5 it works really well and should be faster and capable of handling a lot more applications then 10.4. but in the end its preference. give it a try its easy to find online for a free demonoid is down otherwise id send you a link.
good luck