First of all, for a given resistance exercise, PROPER FORM IS MORE IMPORTANT THAN WEIGHT! Your objective is to engage as many muscle fibers as possible. This can only be accomplished with proper weight lifting technique. By using improper form, you are less likely to engage every muscle fiber in a given body part (bicep, tricep, etc), resulting in slower, less effective muscle growth.
Secondly, you are FAR more likely to injure yourself! Improper lifting technique is one of, if not, the most common cause of weight training injuries. So if you notice yourself using improper lifting technique as you increase weight, let go of your ego, drop the weight, and KEEP YOUR FORM!!
"I don't live to eat...I eat to live!"