A massive amount, substr has a hell of a lot simpler job to do.

    Benchmark: timing 500000 iterations of regexp, substr...
        regexp: 11 wallclock secs (10.16 usr +  0.00 sys = 10.16 CPU) 
+@ 49236.83/s (n=500000)
        substr:  1 wallclock secs ( 0.90 usr +  0.00 sys =  0.90 CPU) 
+@ 554938.96/s (n=500000)
[download]

gav^