Google Scholar has a reasonable interface, but I find its actual content to be unreliable at best. Downloading references in e.g. BibTeX format, I almost always find significant errors, sometimes in relatively innocuous fields (different formats of a conference name, etc.) but other times in more important fields (authors' names).

It's a great tool, and I use it all the time, but it's certainly no replacement to a properly-managed bibliographic database.