It's possible that Google did. But the timing is interesting.

The patent application that describes Google's Bookmark manager, Methods and systems for personalized network searching, was originally filed on December 3, 2003. I'm not sure of the exact start date for Del.icio.us, but the Wikipedia entry points to late 2003.

The patent application describes "annotations" which sound very much like tags from their examples. Here's one:

Searching annotations comprises searching the user-entered annotations using the search query 114 submitted by the user 112a. For example, a user 112a may enter the term "boat" as an annotation for a page comprising marine supplies. If the users 112a enters "boat" as part of the search query 114 utilized by the search engine 120, the page with the "boat" annotation will be returned by the search annotations component.

So, was it cloning, or was it an idea that was in the atmosphere at the time, that more than one source picked up upon?

The patent application also provides for returning these annotation with search results:

Other operations may also be performed on the results based at least in part on user-specific information. For example, the results may be interleaved, merged where necessary or desired, presented with annotations, or presented in other ways that provide useful information to the user 112a.