I have noticed that Amazon supports online management of collections. It is possible to create a new collection and add/remove Kindle e-books and personal documents from an existing collection. In addition, if you have a large library, the restriction on selecting a maximum of ten documents at a time has now been removed. I still think Tolino’s online content management interface is more intuitive and easier to use. Tolino's web reader is integrated into online content management and it is possible to view/change e-book covers.
Update: I forgot to note that Tolino's online content management allows the uploading of documents from a local hard drive. As far as I can tell, Amazon doesn't support the feature. The only way to send documents wirelessly to a Kindle e-reader is via either the Send to Kindle application or email.