If you get the account there are extra editing features on the web site, including copy/paste for popplets. The payed for iPad app can access local and web side Popplets. Unfortunately you can't copy between the site and iPad. You get the ability to create 6 Popplets with the free web account.
There are still a few bugs. I had a stuck web side popplet that I could not delete using the iPad. It crashed the app. I had to log onto the web site, fix it, go back to the ipad and log out/in to get things working again. YMMV
It is really confusing that they call the both the document and the individual boxes popplets. I tried to alleviate that by capitalizing when referring to the documents.
If Popplets works for you, take a look at Corkulous. It's essentially a big cork board that you can put pictures, notes, labels, and other stuff on, then rearrange any way you like. It's prettier, more versatile, and less bug prone than Popplets, but there are no web site or collaboration options.