I think that you GPA will matter somewhat in any engineering field, at least as far as needed to get that first job. A lot of things can go into whether you get a job, but there are really two parts to getting a job.
Part 1: Get an interview.
How do you do this, well, it can be hard. Make sure you know how to write a good cover letter and resume. If you are right out of college, a 3.0-3.5 will probably be a good range for engineering. More is better, but make sure you are involved is some activities. All of this looks good on a resume and will help you get that interview.
A lot of people will tell you the extra-curricular stuff doesn't matter. They are wrong and here's why: I made interviewing my last year a goal. Tons of companies came to campus and I interviewed with as many as I could. Some of it was practice, some of it was the "I don't know really what I want to do". Bottom line is this...the first question asked of me in well over half of my interviews was "So, what's it like to be in a big college marching band?". I put that on my resume, and was frequently asked about it. It always helped me break the ice a little bit talking about a subject that I was an expert at and the interviewer knew nothing.
I went to a good engineering school. At the time, no work experience was required to get a degree. Now you must have at least one internship to graduate, so work experience really can get you noticed and get that interview. We look for candidates who have a decent GPA (3.0 or better), work experience and some out of class activities. If you don't have all three, don't plan on even getting that phone interview.
Part 2: The interview
Now, you have the interview, don't screw it up. How do most people screw it up? Let me tell you....they can't communicate. If you are in engineering, you better know two things.
1) How to communicate verbally with all kinds of people
2) How to write. If you can't write....get the hell out. I've been an engineer for 9 years and the vast majority of both jobs that I have had are all about writing. Reports, email, proposals, presentations, manuals, work instructions, you name it, I write it.
The writing part obviously isn't so important in the interview, but you had better be comfortable and able to have a good discussion with the interviewer. The stereotypical engineer who works in a lab all day is done...you need to be able to work well with others and communicate. Practice interviewing if you need, but make sure that you are good at it. It will really help.
Well, I didn't plan on a dissertation, but I hope that it helps someone.
TBW