class Array

(1..10).to_a.split { |i| i % 3 == 0 } # => [[1, 2], [4, 5], [7, 8], [10]]
[1, 2, 3, 4, 5].split(3) # => [[1, 2], [4, 5]]

or the result of an optional block.
Divides the array into one or more subarrays based on a delimiting +value+

def split(value = nil, &block)
  inject([[]]) do |results, element|
    if block && block.call(element) || value == element
      results << []
    else
      results.last << element
    end
    results
  end
end