File.expand_path seems to be much slower under ruby 1.8.0 when compared to 
ruby 1.6.8, tested under debian unstable

$ ruby -v
ruby 1.6.8 (2003-07-09) [i386-linux]

$ ruby1.8 -v
ruby 1.8.0 (2003-08-10) [i386-linux]

Testing code:

1.upto(100000) do
   File.expand_path("linux/blabla")
end

$ time ruby bench.rb

real    0m0.737s
user    0m0.590s
sys     0m0.150s

$ time ruby1.8 bench.rb

real    0m4.370s
user    0m1.590s
sys     0m2.740s

Idan.