Now that I have been running OS 10.6 (aka. Snow Leopard) on my 2006 MacBook Pro for a week. I can offer my opinions of the latest OS X. Twitter followers had heard me complain that my MacBook Pro was very slow with certain apps, including those that others had raved about for being improved and much speedier.
If you read my post, Snow Leopard Now Installed, you will know that I spent some time examining all the Extensions, Input Managers and Plug-ins, to ensure compatibility with OS 10.6 before I upgrading my MBP. So I don't believe the application slowness was due to the incompatibilities of Extensions, Input Managers or Plug-ins.
One thing that may cause my poor experience is the fact that my MBP has an Intel Core Duo rather than a Core 2 Duo, so it is not a 64bit processor.
As readers of my other post; mentioned above, or people who had installed OS 10.6 know, the update has recovered about 50% more free space on the boot hard drive. This savings may have hidden the fact that applications are occupying more RAM than before, which may be another reason why my MBP is slow. As my MBP has a maximum RAM capacity of 2GB, which I had already maxed out.
So what I decided to do was to sell my tired MBP and replace it with one of the latest MBP 15" model.
My conclusion is that if you do not have one of the later Macintosh from late 2008, there is really no need for you to upgrade to OS 10.6. You can hold off on the upgrade until there is a requirement from one of the applications you use to upgrade. Even then you should read my post, Snow Leopard Now Installed, and do the check of your Extensions, Input Managers or Plug-ins for incompatibilities before upgrading.