Could it be hard disk issue? I also install a lot of applications in my MacBook Pro and it's working fine. If you don't mind, reinstall Leopard. Oh ya, when I 1st bought my Mac, it's in tiger and the staff upgrade it for me to Leopard. Still I'm not happy with what they do, so I reformat the notebook myself and install Leopard as a fresh installation. Maybe the upgrade from Tiger to Leopard is causing the problem for you.

If you don't know how to format and reinstall, you can bring back to the shop and tell them to install Leopard as a fresh installation. I think is free of charge. Between, REMEMBER TO BACKUP YOUR IMPORTANT DATA FROM YOUR MAC. If not, your wife will kill you for that. Hehe...