Is there really any reason to use Leopard?

a) No
b) Yes

I had the same problem with my G4 PowerBook. It also helped to move all my files to an external hard drive (leaving only the apps and OS on the laptop’s HD).

Applications that you never use do not make your Mac slower, with the following caveats:
1/ some applications like to have a helper program that starts at login. This does slow down every login, and sometimes makes your Mac slower also the rest of the time. You can see if you have these in System Preferences -> Accounts. By the way, you will see iTunesHelper there, I think you can remove it. It must be useful for starting iTunes automatically when you plug an iPod or to get your podcasts for you in the background or something. iTunes works without it.
2/ Having had an almost full hard drive for a long time can create fragmentation and make your Mac appear slower than it should. A fresh install will solve this.

I find spotlight to be more snappy on Leopard, and already some applications are out that no longer work on Tiger, but it’s perfectly doable to use Tiger for everything in 2009.

I guess the thing to bear in mind is that a lot of 3rd party developers are developing for only Leopard now – however if it’s a major enough app you should be able to get Tiger support for a little while longer…

I have a feeling with Snow Leopard it may be a different ball game (and I hereby trademark the blogger pun ‘Slow Leopard™’ for how it runs on older machines ;)

That said there may be a tradeoff where a faster Intel-only OS may run faster on older hardware than Leopard does, because it’s been more highly optimised.

I’m going to upgrade towards the end of this year when my 3-year Applecare runs out on my 2Ghz MB.

I’ve found that Leopard runs faster on older machines than Tiger does. It seems to be be much more refined. Spotlight searches, printing, graphics, and PDF handling are noticeably improved. I use Quick Look frequently to preview files. Your MacBook should certainly be able to run Leopard very well.

The #1 key factor to having either Tiger or Leopard run well is RAM. 1GB is the bare minimum. 2GB is needed for things to run really smoothly. If you don’t have enough RAM, and if your hard drive is too full to provide enough virtual memory, then things will surely bog down.

A lot of applications actually run faster on Leopard. I would not personally run an old OS for performance gains. It’s not like Windows where XP is tons faster than Vista. As time goes on Mac OS actually gets more optimized and runs faster, not slower, in general.

My 1.67 GHz Powerbook G4 with 1.5 GB of RAM runs Leopard without any problems. It might be very slightly slower than Leopard, but I like Leopard better anyway. It sounds like your computer is having a different problem. You’d probably get more results from following pascal_cuoq’s advice above, then maxing out the RAM like simpleD suggests.

Doing any or all of the following will likely be more helpful than going back to Tiger:

1. Check for programs loading at login under Apple Menu > System Preferences > Accounts > Login Items. Delete everything but iTunesHelper. (Note that unchecking the check box next to the application will NOT prevent it from loading at startup.)

2. Make sure your hard drive has lots of free space (at least 10%).

3. Since your computer runs fine most of the time, it’s possible that one particular program is making it slow down. You can use Activity Monitor (in Applications > Utilities) to find out whether one program in particular is giving you trouble.

4. Make sure you’re quitting applications when you’re done with them. This may not apply to you, but many people leave Mac applications running all the time, because they’re used to just closing the window on Windows. On the Mac, those applications remain active unless you explicitly quit by pressing command-Q or choosing Quit from the file menu. You can see the active applications by holding command-tab or looking in the dock.

5. Back up your stuff, reformat your hard drive completely, then reinstall Leopard. Add back only the programs that you need.

6. Add more RAM. Ideally, you should have 2 GB of RAM.

Hobbes,

when I first replied, I was focused on the feasability of going back to Tiger on a Leopard-capable Mac. Thinking a little more about it, and seeing the other replies, I would like to change my reply a little (and concur with the others): my mom’s first-gen 2GHz MacBook works great with Leopard and it wouldn’t be more usable with Tiger.

Actually, that MacBook was good, but not great, when it had 1GiB of memory. I recently upgraded it to 1.5GiB and this is when it became a pleasure to use. Purists will tell you that it’s better to have a pair of identical SODIMMs installed on your MacBook. This is true, but this effect (up to 5% faster on some specific computational tasks) is much less than the effect of having 512MiB more working space for the system.

If you have 1GiB or less of memory, upgrade! On the MacBook, it is easy: 3 screws and a lever (you can find a step-by-step guide online, even directly from Apple in this case http://support.apple.com/kb/HT1651). The 1GiB SODIMM I bought was 10 EUR in a Mac shop that was able to guarantee that it would work in the MacBook (you may have to pay 12 for yours, I was lucky). If you want to do it at minimal expense, replace one SODIMM with a 1GiB one. If you want to be done with it (and the satisfaction of knowing everything is as fast as it could), replace both.

You can check the amount of memory currently installed in your MacBook in “Apple menu -> About this Mac”.

The most recent version of Photoshop only runs on Leopard. Third party is a major issue unless you just check your email and the web. Even little free programs might only be developed for Leopard.

I’ve got an intel 2.0 with 2 gigs of ram and it runs Leopard as smoothly as it did Tiger.

One of my cheapo mp3 drives was no longer recognised after I installed Leopard.

I doubt it could be technically proven, but in my experience, a fresh install of leopard works so much nicer and faster than a Tiger—>Leopard upgrade. You could give that a shot.