Absolutely. It helps with things like the Trojan issue that was discussed earlier. You should run with as little privilige as possible. I found that creating a seperate admin account was not actually enough, and had to add one more step (as an admin account):
sudo chown -R root:admin /Applications
sudo chmod -R o-w /Applications
Then run fix permissions to fix anything you broke

Those two steps ensure your default account cannot even write to the Applications directory.
In OSX it is really not inconvenient to have a seperate administrator account. You'll notice two things:
1) When you have to do something with admin priv, you are now asked for a username and password; you don't need to use FUS or anything like that
2) When you try to use finder to do something in a system directory, you will be told you don't have permission, and do you want to authenticate, if you say yes you are again asked for a username / password.
So even with the changes above, you can still drag an app into /Applications, you'll just have to give a username and password to be allowed to do it.
On the plus side, the account is denied access to anything outside of /Users, so it really cuts the damage a virus, trojan, or worm can do to your system.