Lieter Report answered a question about how to write a personal statement for philosophy graduate programs. The comment about masters applications I thought was interesting. If your thinking of applying to Grad school READ Warfield's comment. The majority of my research suggests that his weighting of the topic is basically correct.
The Lieter Report:
My own views (having done PhD admissions four or five times in the last decade) are as follows: (1) the personal statement should make clear what the student's philosophical interests are (at present) and how those interests make the program to which the student is applying a sensible choice (in this context, mentioning particular faculty can make good sense, and show that the student has given some thought to why he or she is applying to a particular program); (2) one can't really "do philosophy" in a personal statement, but one can certainly offer examples of particular philosophical problems (e.g., mental causation) or topics (e.g., Stoic ethics) that convey both the depth of undergraduate preparation and complement the explanation of why the candidate is applying to a particular program; (3) deficiencies in GRE scores or GPA are most persuasively addressed by your faculty recommenders (students ought to discuss the issues candidly with their advisors), but it is certainly not inapprpriate for the personal statement to address these kinds of issues--but statements of the form, "I am a much better student than my undergraduate GPA would suggest" are useless; more pertinent is factual information--e.g., "my overall GPA was dragged down because I was an engineering major my freshman and sophomore years; but when I switched to philosophy, my GPA rose to a 3.8" or "my junior year grades fell significantly when my mother died unexpectedly; I believe my sophomore and senior year grades are more indicative of my philosophical ability."
The personal statement may certainly say something brief about the student's professional and personal goals: most commonly, a career as a college teacher of philosophy, or sometimes personal edification and enrichment. I would not spend much time on this: presumptively, those who apply for PhDs in philosophy want to teach the subject. The items noted above (1-3) are generally more important for an admissions committee: i.e., what is the student interested in, and does his or her interests fit with what our program has to offer.
I think that all of Brian's advice is spot-on. To add a few minor points:
(1) Have a faculty member (best would be somebody who has been involved in graduate admissions, if your school has a grad program) look over your statement.
(2) Have the majority of your personal statement be the same for all places. But it's good to leave open a bit of space at the end of the statement to describe why program X in particular fits in well with your goals and interests. This is something you ought to be thinking about anyway as you're deciding where to apply. Showing that you know something about this dept. in particular and have given some serious thought about these questions will make you look more seasoned and serious.
(3) Let me repeat the call not to wax poetic about the wonders of philosophy and the philosophical life. Many philosophers have a taste for desert landscapes in prose; don't make them cringe.
Two things to consider that haven't been mentioned yet:
(1) I was told by a number of people that Ph.D. applicants with an M.A. already are usually expected by admissions committees to have a clearer idea of the sorts of issues upon which they'd like to focus. And so, that part of the applicant's personal statement would reflect such clarity by perhaps being more specific (e.g., instead of "I'm really interested in ethics," the applicant might say something like "I'm really interested in the extent to which moral psychology ought to inform our more general moral theorizing").
(2) I did my undergraduate work at a place that (I'm betting) no one on any admissions committee had ever heard of. So part of my personal statement was a description of the sort of training in philosophy that I actually underwent as an undergrad. I'd encourage applicants in similar situations (i.e., going to colleges that might lead an admissions committee to wonder about the sort (and strength) of philosophical background you really have) to do the same.
I should add one final word of advice: trust your advisors. They know (better than you do) what admissions committees will find most interesting about *you*. So if a professor of yours tells you to change part of your statement, change it.
From my experience doing admissions at Notre Dame over the years, I think far too many candidates spend quite a bit of time on their personal statements that should have been spent on their writing sample. The writing sample is at least 50 times as important as the personal statement. This is true especially in making tough decisions late in the admissions process about who gets in now and who goes to the wait list.