I had this dress custom made to my measurements by eShakti (few items ever fit me right off the rack in this country), but the midi-length of it was woefully unflattering. Even with heels. I look stumpy. I mean, I AM stumpy, but dang.
I pulled out my sewing machine and hemmed to make it hit right at the knee and as you can see in the photo on the right, my legs look much longer and I look taller overall (and it's still modest enough to wear anywhere). It only takes a few inches of excess fabric to make you look dumpy when you're petite.
If you're worried that hemming is hard, all you really have to know is how to sew in a straight line with a machine (though this dress is a full-circle-skirt bottom, so it was a *slight* curve, but it is still basically sewing in a straight line). It's also really fast, even when the circumference of the skirt/dress is over 60 inches *cough*
If the length of a garment is the only reason why you don't wear it, or would otherwise purchase it, then hem it. OR, if you'd rather put your hand in a blender than sew, take it to a seamstress. It's one of the cheapest alterations you can have done, and will probably cost you less than $20. A lot of dry cleaners will offer this service as well. Of course, doing it yourself will in the long run save you lots of money, especially if you learn other alterations as well (and sewing is just a practical skill to have... though don't tell anyone if you can sew. Suddenly everyone will have annoying favors for you, like hemming their curtains, and expect you to do it for free. TELL NO ONE. Keep it secret; keep it safe, my hobbit friend.)
I just use a basic sewing machine model, a beginner Singer model you can get for less than $200. But I got my money's worth (I also quilt, make stuffed animals for my kids, sew pillows, and do craft projects in addition to altering my clothing).
Because hemming is so basic (measure and cut the length you want to remove, just roll or fold the fabric so you don't have an unfinished hem, pin in place or use an iron to press in place, and sew), I decided a tutorial on that would be insulting to my readers' intelligence. To put it into perspective, I was doing this as a child, and most of your clothing was probably entirely sewn by a malnourished 6-year-old in China, so I trust that an adult can do a basic hem without photos of the entire process.
I also realize that a lot women do prefer the past-the-knees midi-length, and that's fine. But I haven't met anyone shorter than 5'4" that I think can pull that off better than knee-length. So there's my gratuitous opinion on that.