Undergraduate / MIT International Transfer Essay "Why MIT?" [3]

I would say in the second paragraph try and make it slightly more specific, name off some actual research you found that was interesting or mention the topic of some of the articles you enjoyed. Also in the third paragraph I would recomend cutting out the part about you not having to study hard and perhaps replace it with something along the lines of not providing you the challenge you need to succeed.

Undergraduate / 'Fifty-two' - Standford - Intellectually Engaging experience [5]

I think Stanford wants to see how the experience challenged/fascinated you intellectually. I believe that it would be much more on key if you focus your essay on your interst in the biology of the guppies. And less on the story of getting the guppies and them being pets. I think if you address the prompt a little more appropriately you will have a very unique and fun story.

Hope that helps.

Undergraduate / Stanford: Profile questions- favorite books, significant issues, etc [8]

I think that you can getaway without using complete sentances on a question or two if the content really distinguishes you and you want to emphasize it. But for the rest some eloquent wording could help.