C++: 388 characters
#include
#include
#include
#include
#define w v[y][x]
using namespace std;size_t y,x,*z[]={&y,&x};int main(){string p="^v<>",s;dequev;
while(getline(cin,s))v.push_back(s);while(x=v[++y].find_first_of(p),!(x+1));int
i=p.find(w),d=i%2*2-1,r=i/2;do while(*z[r]+=d,w=='/'?d=-d,0:w==' ');while(r=!r,
!strchr("#x<^v>",w));cout<<(w=='x'?"true":"false");}
(318 without headers)
How it works:
First, all lines are read in, then, the laser is found. The following will evaluate to 0 as long as no laser arrow was found yet, and the same time assign to x the horizontal position.
x=v[++y].find_first_of(p),!(x+1)
Then we look what direction we found and store it in i. Even values of i are top/left ("decreasing") and odd values are bottom/right ("increasing"). According to that notion, d ("direction") and r ("orientation") are set. We index pointer array z with orientation and add the direction to the integer we get. The direction changes only if we hit a slash, while it remains the same when we hit a back-slash. Of course, when we hit a mirror, then we always change orientation (r = !r).
