If you're like I was, you're thinking the answer is obviously "no" for the following reasons:
Oh wow, in thinking that through I think I've convinced myself that I don't need a personal trainer :-) But yet working with one made a huge difference for me, so I'll give you the positives now:
So for me, it turned out that a personal trainer wasn't a luxury but a necessity. I had tried many times to lose weight, some more successful than others. I'd like to think that it was a sign of strength for me to admit I had a serious problem, I was weak and that I needed help. Ok, in all honesty the 70 pounds I've lost since last year is still a bit new and I haven't proven that it will stay off. But this time definitely feels different. I'm happy with my health, the way I feel, the way I look, and I feel like it is a lifestyle I can keep up indefinitely.
If you just have a few pounds to lose and need to trim down, perhaps the personal trainer isn't for you. There are also many examples of people who go it alone and have success. But if you have significant weight to lose, ask around, do your homework and consider finding someone that can help you from both a dietary and an exercise perspective. If you find a good trainer, you won't regret your decision.