I'm currently doing the special k slimmer waist for summer challenge in a desperate bid to loose a bit of weight for my wedding in 4 weeks! It basically consists of eating a bowl of special k for breakfast and then replacing either lunch or dinner with another bowl and it claims to make you drop a jean size in 2 weeks.

What it doesn't tell you is that it causes you to get mouth ulcers and chronic headaches!

Have any diets you've been on caused any side effects and was it worth it?

I loathe the diet concept but couldn't help reading your post! ;) I think by their nature 'diets' as opposed to 'a healthy diet' that's part of a healthy lifestyle and sustainable over a lifetime are unbalanced, thus will cause your body to kick up a bit of a stink. I would favour your usual (presumably balanced) diet with portions halved; cut out incidental calories by cutting out milk coffee/tea and alcohol, and still have a Freddo or a Magnum mini at your most needy time of day so your body doesn't resent you. You'll need to reduce weekly intake by 35,000 kj to lose 1kg a week. Impossible to leverage with food alone so you'll need to amp up the exercise!
Sorry, simple answer is food restriction has caused side effects - no it wasn't worth it :)

Can I finish that with, if that's your pic, what are you doing trying to LOSE weight???