I used a personal trainer for 3 years and I can't say I'd really recommend it. Definitely had it's advantages, but too many disadvantages to be worth the cost.
High turnover - I had about six different trainers during that time.
They all picked some random exercises for me to do whereas I'd rather have a well thought out schedule.
They are all flakey, lots of appointments cancelled last minute for "family emergencies."
Two asked me out on dates. I guess this would be an advantage for some, but I was interested in getting fit, not picking up men.
One was kinda mean to me.
I found going to yoga classes MUCH more useful.