(1) Some people say the DevTools slow things down, so If you don't really need them, re-install X without the DevTools. (Maybe you can backup the /Developer/Applications/ folder, it holds some interesting apps that run without the rest of the DevTools).
(2) Add more RAM
(3) Wait for Mac OS X 10.1 in September. It looked hella fast in the Stevenote yesterday.
If you installed the DevTools before the 10.0.1 update came out, the speed increase was due to pre-binding done by the DevTools installer. (The original Mac OS X installer on the CD doesn't do pre-binding.) Newer updates of the Mac OS X also use pre-binding, so I doubt installing the DevTools will speed up versions newer than 10.0.1.
Besides adding more RAM to solve your problem, you might try using a high speed connection. When I moved a few months ago, I had a span of about a week during which I had to use dialup. I had a cable modem before the move and have DSL now. I can tell you (and have heard from others as well) that having X connected through the cable or DSL modem sped things up considerably from when I used the dialup connection. Don't know why. Just is faster.
And, I had thought that my 1998 Powerbook w/ X was just slow when I'd use it on trips... Turns out the same is true of the Powerbook. I hooked it up to my home network and noticed a pretty big speed jump.
You didn't mention which type of connection you are using in your original post, but if this applies - hope it helps.
I believe this is true: I used Mac OS X during the first month with a dial-up connection, since the end of April I have Cable, and I did notice a speed increase. I've heard PPP/dial-up isn't fully/correctly implemented in OS X (cfr. Classic compatibility), maybe there are some speed issues with it as well.
Also a little speed boost can be done by running prebinding, I think it sortof is like rebuilding your desktop db, not positive though. I just know that at least my apps launch a little faster after prebinding. You can get xOptimise on versiontracker (I don't remember the cli command).
Basically, the prebinding process just creates some kind of a "roadmap" which shows the system which application uses which libraries. Once an application is started, the system looks into this roadmap and loads the needed libraries into the RAM. Now, if you installed stuff and moved some files around, it can happen that this roadmap gets outdated. So once you launch an application, the system cannot immideately find a needed librarie and has to search it. However, with updated prebindings, this doesn't happen. I heard that one of the reasons 10.1 application startup times is that it loads most of the libraries into RAM at startup...if this is true, we just might need some more RAM.
If you install new software in OS X, like updates to the system, there is the final step "optimizing the system". In this step, the prebindings are updated. So installing DevTools 10.0.0 or any X update might give you the feel of a small speed increase which will vanish after some time without regularly updated prebindings. DevTools 10.0.1 however changed some graphic libraries and in fact it speeded up some Aqua elements...although the speed increase is far from beeing as dramatic as what was shown with 10.1 at wednesday.
So what you can do: Install DevTools 10.0.1
REGULARLY update your prebindings:
You can do this easily with a tool called XOptimize (search it in version-tracker.com) or just gain root-access and type
update_prebindings -root / in the console, with the -verbose option if you wanna see what's going on.
Also, there is a tool which manages all the logfiles and stuff like that, which can bring another very small speed increase if it is used regularly. It basically just runs maintainance scripts which are executed daily, weekly and monthly from OS X, but only if the Mac is turned on at the critical time where the script SHOULD run (for example at midnight). I don't recall the name of the tool but I am sure the others in this forum will post the name.