General talk about software patterns

["Jan Hannemann" <jan AT cs.ubc.ca>]

I'm wondering which patterns are actually used more frequently than others
in practice(*). In particular, I'd like to know which the top-5 (or top-10)
Gang-of-Four patterns(**) are in terms of number of pattern instances found
in practice. I do realize that this is hard to determine objectively, but
subjective rankings are fine, too.

For example, I think it is pretty clear that Interpreter is less commonly
used in practice than, say, Observer. 

Are there by chance even research papers on this topic available? Or on
related topics (empirical study of patterns in the wild)?

Opinions are welcome as well. A few years back I spoke to one of the authors
of the GoF book and he gave me this informal list of what he thought were
the top-9 according to his experience (most commonly used on top):

Observer
Composite
Singleton
Abstract Factory
Visitor
Adapter
Factory Method
Template Method
Command

Can you confirm this list, or do you have different experiences with
patterns used in practice?

Thanks!

--Jan


PS: To provide some context: my research involves design patterns (in
particular, the GoF patterns) and I want to make sure I focus on patterns
that are actually used in software development.

(*)  With "in practice" I mean "in real-word software systems". 
(**) I'm only interested in the GoF patterns.