Something I dislike about purchasing an app on the iPad is that there is no queue system in the App Store, so if you want to purchase a few different apps, you type in your password on the first app to download it, and the App Store closes and the the Home screen slides away taking you far from the App Store icon to rest at the page where your new app will live. One solution is multitasking on iOS 4, or even folders (if all your icons are in folders and you only have one or two pages then its not difficult to swipe back to the App Store) but you can't do this on the iPad (yet).
Something I've discovered is that after the App Store closes, right as the screen is about to swoosh you away to Page 11, if you quickly put your finger down and 'hold on' to the Home page, you won't move away and when you let go, you'll stay put and you can immediately click on the App Store again while the program downloads and installs. It is slightly faster than waiting to go to the end page and then clicking the Home button to go back.
[crarko adds: I haven't tested this one. This problem should become moot in a month or so when iOS 4.2 comes out for iPad.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20101008013424235