What specifically causes slow directory listings in OS X? Finder, Save As boxes, etc

Question

I have a very specific problem with my laptop in terms of speed. A lot of things happen very quickly on it, especially since I started using tools like Onyx etc to maintain it. But my Finder is notably slower than the machine in general.
To give you some examples, sometimes when I'm in column view and I click on a folder, it can take several seconds before the list of files appears in the next column. When I go to File > Open inside an application, it seems to take forever for the box to be propagated with the list of files in the directory. Changing directories inside a box like this yields the same result, the whole list goes white for several seconds before the new directory appears.
Spotlight has similar issues - it always finds what I want, but it seems to take a very long time. Sometimes it's several seconds before any results appear at all, and other times some results appear straight away (usually applications) but I have to wait considerably longer before documents also appear in the list. Launching applications from Dock can take a while, with apps sometimes bouncing up to 10 times before opening. Interestingly, if I quit an app and relaunch it later, it takes far fewer bounces for it to open, it's only slow the first time I launch after a reboot.
You get the general idea. File and directory listings are very slow, and far slower than almost any other task I want this computer to do.
I've defragmented both used and free space, rebuilt the directory several times, verified with no errors, repaired permissions with no errors, and I'm stumped as to what could be causing this kind of problem. Activity monitor doesn't report that I have any page outs and CPU isn't running high at all so it's not that. I do regular smart checks and surface scans to make sure there's no corruption or anything like that and they consistently tell me everything is fine.
I'm pretty stumped.
MAcbook is a black late 2006 macbook 2,1 with 2GB RAM (max), running 10.6. Also, when I installed 10.6 a couple of years ago it was far faster than it is now, before anyone tells me I simply don't have enough RAM. The computer behaves this way even when it's fresh from a rebook with 75% of RAM free, so that's not the issue.
Any ideas?
EDIT: My SL partition is 100 gigs, 60 used, 40 free. 39.5 contiguous free space in one block, hardly a desperate free space situation...

Answer 1

I used techtool pro, and I did so specifically in the hopes of solving this problem. It does seem to have sped up the computer somewhat, but more in the sense of how quickly it opens and saves files, which when you consider the result of defragmenting seems to make sense. Hasn't helped with this Finder problem in any way whatsoever though, or with the opening of apps from the dock.
EDIT: I don't want to get into a debate about this here as this isn't the subject of this thread, but built in defragmentation only handles files up to a certain size, and when you're a producer like myself working with DV and WAV files which can get into the hundreds of megabytes, that doesn't cut it. The TTP defragmentor specifically lists these files again and again as the ones which fragment, so it's obviously not a totally flawless built in system.
Anyway the slow directory listing issue was present long before I touched the drive with any such tools and the tools made absolutely no difference to that problem, for better or worse.