Syncing research papers with iPad is a great idea. It is just sad that Mendeley fails miserably in the execution.
You can sync your citations and files with Mendeley, but viewing PDFs is useless. You cannot view full screen in landscape mode, meaning that you can only view an A4 paper at half its width (in portrait mode). This ensures that as far as reading papers are concerned, Mendeley is useless.
Also, if you organized your papers in folders, the iPad app magically collapses it.
You are much better off making a special Dropbox folder and sorting your papers in there. Not the perfect solution, but better than this...
This App is a waste of time and left me severely disillusioned.
Dcm1984b about Mendeley (PDF Reader), v1.3.3