Upward trends are great. Most applicants have a j-curve with the lowest gpa in sophomore year.
I have to say that I don't see many retakes. I tend to run down the column of letter grades looking for C+ or lower & then look across to see what the course was and when the course was taken. I might not even look to see if the course was retaken. One poor grade is forgivable. One horrible semester can even be overlooked if the applicant has a story to go along with it. A horrible college career (before the applicant was pre-med) can sometimes be overlooked if the applicant has a 4.0 post-bach of 30 credits or more and several years of work experience (goes to the maturity factor). In all these instances of below median grades, you want to see MCATs that are at or above the school's median.