Go is pretty slow right now. I wrote a prime number finder in Go and Ruby 1.9 and Ruby smoked it. Granted that's probably mostly due to all the math in Ruby being C, but still, you can't just say that Go is faster because it's compiled before hand.
I'd love to know what I screwed up. The results surprised me:
https://gist.github.com/pkulak/99d2d5a5968b5fc03754
https://gist.github.com/pkulak/909d882614e0781e4525
bender:Desktop phil$ time go run primes.go
Found them! 78702
real 0m21.349s
user 0m21.304s
sys 0m0.033s
bender:Desktop phil$ ruby -v
ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.4.0]
bender:Desktop phil$ time ruby primes.rb
Found them! 78702
real 0m7.656s
user 0m7.651s
sys 0m0.005s
bender:Desktop phil$ time go build primes.go
real 0m0.269s
user 0m0.231s
sys 0m0.033s <...>
for j := 2; j < limit; j++ {
if i % j == 0 {
found = true
<...> math.Mod(float64(i), float64(j))
i%j
$ time go run primes.go
Found them! 78702
real 0m0.835s
user 0m0.787s
sys 0m0.039s
$ time ruby primes.rb
Found them! 78702
real 0m21.013s
user 0m21.005s
sys 0m0.016s(I understand that you did because the original poster did it)