okay yea, it does seem to be 10x slower:

                                                        
root# julia speed_test.jl 10                                                                                           
elapsed time: 0.007485235 seconds (139956 bytes allocated)                                                             
elapsed time: 0.009702895 seconds (279740 bytes allocated)                                                             
elapsed time: 0.000283116 seconds (0 bytes allocated)                                                                  
elapsed time: 0.001188023 seconds (160000 bytes allocated)                                                             
root# vi speed_test.jl                                                                                                 
root# julia speed_test.jl 10000                                                                                        
elapsed time: 0.022272985 seconds (139956 bytes allocated)                                                             
elapsed time: 0.128069668 seconds (25557260 bytes allocated)                                                           
elapsed time: 0.015917311 seconds (0 bytes allocated)                                                                  
elapsed time: 0.113222569 seconds (25437328 bytes allocated)   

                                                                         
root# cat speed_test.jl                                                                                                
N = ARGS[1]                                                                                                            
                                                                                                                       
a = BitArray(int64(N))                                                                                                 
                                                                                                                       
@time for i in 1:10000                                                                                                 
    Base.bitarray_rand_fill!(a, true)                                                                                  
end                                                                                                                    
                                                                                                                       
@time for i in 1:10000                                                                                                 
    Base.bitarray_rand_fill!(a, rand)                                                                                  
end                                                                                                                    
                                                                                                                       
@time for i in 1:10000                                                                                                 
    Base.bitarray_rand_fill!(a, true)                                                                                  
end                                                                                                                    
                                                                                                                       
@time for i in 1:10000                                                                                                 
    Base.bitarray_rand_fill!(a, rand)                                                                                  
end