My general advice (to our students and others) is that the personal statement may be the least important part of the whole process but inversely proportional with the stress they seem to induce. Bottom line, unless you have a life-altering event that has helped to make you who you are the personal statement is a necessary hoop through which you must jump. Couple of tips:
1) Do not use more than 1 page
2) Do not use 10 font to keep it to 1 page (!)
3) Do not feel compelled to discuss which subspecialty you envision yourself in 10 years unless you're really certain (since ~75% of our residents change their minds - at least once! - during the residency).
4) Please, please, please, have a friend or mentor edit, proof, etc... and please use spell-check to avoid the dreaded typos.
Hope this helps
wnl