I found that when I go to the home screen and there's no spinning network indicator, then my updates are done.
I usually hit update all, then go to the main page and watch the little counter on the App Store icon decrement until it disappears (this is so I don't wake my phone later to find the process has halted because one of the apps is rated 17+ because it has a browser). Then I check it occasionally and wait for the network indicator to stop spinning.
I also have almost all my apps inside folders on 3 pages, so it doesn't take long to page through each page and look for the progress bar on the folders. If you have a lot of pages of apps it might take awhile, but put your apps into folders and the folder shows a progress bar that takes all the apps inside it into account for updates, so that can reduce the time you spend looking at app icons to see if an update is still occurring.