How Can I Increase My Braking Power? I've been reading a bit about riding and braking techniques (http://sheldonbrown.com/brakturn.html) and I'm having some trouble pulling off the hard front brake.

I believe this is the style of brake that I have on my bicycle:


However, when I apply my front brake, with maximum force - it doesn't seem to be nearly enough to send me over the handlebars or skid the tire.  I slow down, but it seems to be fairly gradual.

I've adjusted my brakes myself (possibly, I've done it incorrectly...) but there is very little clearance between my rims.  My wheels both seem to have a very tiny wobble that prevents me from setting my brakes any tighter, but when I pull the brake it feels fairly soft, almost as if the cables have some stretch to them?

My real question here is what can I do to improve my braking time?  Does it sound like I've done something wrong.  I did have the brake pads replaced once before, but they appear to be in good condition.
First off, if anyone has mucked with the components on the bike it's possible that they exchanged either the brake levers or the brakes themselves and produced a mismatch where the levers are not capable of providing enough pressure.  But this shouldn't be a problem if the bike has all it's original components.

And if, when you squeeze the brake levers, they "bottom out" against the bar, that indicates that they're misadjusted or the cables are rusted/worn.  (If, due to wheel wobble, you can't adjust tight enough to prevent bottoming out then you need to get the wheel trued.)

But failing those, likely it's a problem with the brake pads.  First make sure they are squarely pressing against the side of the rim and have not gotten twisted to where they're making poor contact.  And check to see that the pads are not worn down to where the metal pad holder is close to hitting the rim.  (Note that the rear edge of the brake pad will tend to wear faster than the front -- simply because the pad looks good from the front does not mean it is good.)

If the pads are not worn out (and they don't have oil on them or some other such problem) then it's probably just a problem with pads that are too hard and you need new pads that are a little "grabbier".  This is, to a degree, a personal choice thing, as there are different pad materials with different characteristics (and most people don't like pads that grab too much), but it's also true that a given set of pads will get harder and brake more poorly as they get older and more worn.

One last possibility is that you have the rare case of steel rims (usually only seen on very cheap bikes).  Brakes don't work nearly as well on steel rims as on aluminum, and so for steel you need pads that are quite "grabby".