I do have a 5 year plan. It's broken down into shorter term goals (3-6 months, 6-12, 1 year, 5 years, long-term). The act of breaking down my long-term goals and putting them to paper forces me to think more clearly and specifically about how to achieve them. It makes them manageable for me.
The things on my "5 year plan" that really have helped steer me in the direction I want to go are these:
Skills to develop
What I care about in a work environment
Personal Goals
The "skills to develop" section helps me to be honest with myself about what I need to work on. Having these things written down forces me to be honest with myself about what kind of things I need to improve.
"What I care about in a work environment" is a list of values that I have and that I want the companies I work for to share. It helps me determine what kinds of jobs I should take- if a company doesn't share those values (like the need for a liveable wage) then I probably don't want to work for them.
In the "Personal Goals", I try and make sure that the things that are important to me outside of work are being taken into consideration. (For instance, planning to take a vacation). It's the hardest part for me- to make sure that I'm looking out for myself as a person and working toward what I want out of life, not hyper-focusing on my career.
I think the act of writing these goals down forces me to think about them honestly. It can be a big factor in deciding whether or not to pursue a certain position ("Does this job help me advance towards where I want to go?"), or go in another direction.
I don't revisit the plan frequently, but every few months I'll re-evaluate, and see if my goals are being met, or if I've lost focus. Sometimes I've decided that what I've written no longer applies. But in writing this post, I've been looking at an old 5 year plan, and I can say that it helped me a great deal in deciding what path I want my career to go, and how to get there.