The people at Zotero have recently redesigned the website, and it looks very promising. It offers much faster access to your online library. The previous version was next to useless, only offering a list of all your references. In the new version, you can now add and edit records, add to collections and filter on tags.
The option to sort on a column is only implemented for the column ‘Date modified’ (workds really fast), but apparently they will make this possible for the other columns soon. [edit: it is now possible to sort on any of the columns]
The feature I am missing most, the option to sort columns and to search your library is not available yet, but also this feature will be added soon according to a post on their forum. [edit:This feature has now been added. It isn't perfect yet, it seems only possible to search for one word at the time, but a clear sign the Zotero team is working hard to improve the user interface]
Below two screenshots to give you an idea, but better yet, check it out yourself on www.zotero.org.