The guide bushes are a good piece of kit to have and relatively cheap to buy,the green box,brass ones you have shown on your site...I have these,bought off ebay for £12 and the actual bush guides themselves are suprisingly accurate in diameter.
Anyway for some reason? a job I was doing, I needed to route a T joint in two sections of the stock I clamped a straight edge just before the marked line cut,positioned the router so that the 1/2 wide straight flute bit was dead center with the line and proceeded to cut the rebate with a depth of 3/8 the length of the wood.
I then put a 1/2" guide bush on the router base plate,fitted a 1/4" straight flute bit and set the depth to 5/8" and that guide bush just sang though the 1/2" rebate cutting a 1/4" rebate dead center below the 1/2"rebate.
So thats one idea that wins with the guide bushes because if we didn't use a guide bush we would have had to set the straight edge up twice. :wink: