I'm personally impressed with how Microsoft have packaged both the SharePoint Install files and service pack installs. They are intuitive and user friendly. However you have to take note of the following:
1. In a multiple server install i recommend that you install your service pack in sequence, starting with the application servers then the Web Front ends. The service pack will prompt you to restart the boxes after install. Restart the boxes in sequence. At this point note that the boxes are not upgraded with the Service Pack yet.
2. To see that your boxes are not installed, log on your Central Administration
Click on check upgrade status, under Upgrade and Migration to see the status on your upgrade.
As you can see above to upgrade your farm you need to run the command and is not stsadm -o upgrade. It is replaced with psconfig.exe -cmd upgrade see the figure below.