Software updates will not install

When i search for new updates and click 'show details' it says i have 15 new updates but when i click 'install and restart' it restarts and they dont ever seem to appear.
I think it has downloaded them but why after restarting cant i find them?

They may or may not be visible depending on the update. The iTunes 10 update for instance is visible both in the icon and the user interface. Other updates are not noticeable such as the 10.6.6 update which, unless you go to "About This Mac", will likely be unnoticeable. What updates did you install?

Further to vansmith's comment, you can if you wish when downloading updates go into the Menu Bar and select 'Download Only' and the update will be stored in our Downloads folder. When ready, drag it to the desktop, run Repair Permissions, double click to install and run Repair Permissions again when completed.

That way you will know they have been installed.