There is also a bug when using the webimporter on ACM, namely that the title of papers is clipped if there is a colon. For example, http://dl.acm.org/citation.cfm?id=1358628.1358875 would be imported as "The cuetable" (which is, as I just found out, also the title of the website, so maybe Mendeley is looking the website's title instead of the full paper name contained within the site).

ACM digital library import does also not work 100% correctly. It seems to me that, when using the Bookmarklet, publication titles are only imported up to the first colon (if there is any). For example http://dl.acm.org/citation.cfm?id=985692.985698 : using the bookmarklet, the title "Caretta" is imported, even though it's "Caretta: a system for supporting face-to-face collaboration by integrating personal and shared spaces"