Rails has now assumed the #1 gem spot with 20,801 downloads at the time of writing. Just in front of Rake, which have long had a solid lead as a required dependency to Rails. Out of the 11 gems listed on the top downloads table on the cover of RubyForge, Rails is now responsible for the six of them.
Funny side note: The two programmers at 37signals (yours truly and Jamis Buck) stewards 8 out of 11 gems listed on the hit list.