Portfolios: why should I have one?

Portfolios have been around for decades. Therefore, the idea is not a new one. What is new, however, is the new ways technology makes available for us to have well-organised, large-scale, easily accessible portfolios in a variety of affordable means.
However, let us start with what a portfolio is and why we even need one in the first place.
A teaching portfolio is

"is a collection of materials that document a professor's teaching goals,
strengths, and accomplishments.
It contains self-generated material (e.g., a
teaching philosophy statement; representative syllabi, instructional objectives,
handouts, assignments, and tests; descriptions of educational innovations and
evaluations of their effectiveness; textbooks and education-related papers
published; instructional software developed; teaching workshops and seminars
presented or attended).
· teaching products (e.g., graded assignments,
tests, and reports; scores on standardized tests; student publications or
presentations on course-related work).
· information generated by others
(e.g., summaries of student, alumni, and peer evaluations; honors and awards;
reference letters). Some items may be mandated, others may be included at the
professor's option."

(from www.utexas.edu/academic/cte/teachfolio.html )
For more details on what to include in a portfolio and for the steps to compile one, here is a short and snappy article: http://www.utexas.edu/academic/cte/teachfolio.html
Keeping a portfolio is beneficial for many reasons: First, it is the best way for a teacher to evaluate and trace his progress as a teacher. Besides, it can serve as a basis for promotions in your career or evidence of your achievements if you consider looking for a better opportunity in other places. A teacher can also use his portfolio as a reference or guide to come back to to solve some problems: If you have a problem motivating your students, you can go back and find materials, activities, ideas you used before. Your portfolio can also serve as a valuable guide for new teachers to follow.
Keeping a portfolio is quite easy. You can have drawers or folders to keep your files if you are "old school" or you can type, scan and store your files in your computer. Always remember to keep a back-up copy of your portfolio. You can trust a computer as much you can trust a wolf beside a lamb.
You can also download software specifically designed for creating resumes and portfolios: http://www.aurbach.com/Toot/index.html
NB: it might, however, not work properly if you are using Windows XP or later.
So do you keep a portfolio? Do you think it is important to have one? What do you keep in a portfolio?
I am keen on knowing about what you think!

References: http://www4.ncsu.edu/unity/lockers/users/f/felder/public/Columns/Portfolios.html
http://www.utexas.edu/academic/cte/teachfolio.html