<p>1) Anywhere from 4-7 years, depending on the field. Technical PhD's tend to be quicker to do than non-technical ones (i.e. the humanities). There are some (ingenious) people who get a PhD done in a year or less. Then there are some who literally can literally take decades (that is not an exaggeration). </p>
<p>2) As you can imagine, pretty high. Although it should be clear that what is really important is your GPA in classes relevant to the field. If you're going to go for a PhD in Chemical Engineering nobody is going to care about what your grades are in a Art History class. Admissions also depend very strongly on your research potential. If you have stellar grades, but you can't demonstrate strong research potential, you will have difficulty in getting admitted to the better programs.</p>
<p>3) Roughly speaking, I would say that about 1/3 to 1/2 of all people who enter a PhD program will eventually get their PhD. It depends on the field - technical fields tend to have higher rates of successful PhD attainment than nontechnical fields. This is true for a number of reasons - the greater research funding available in the technical fields which means that there is a great availability of stipend money and RA-ships that can keep students fed and clothed, the shorter time it takes to get technical PhD's (the longer a program, the greater the chance that people will drop out along the way), the greater proportion of foreign students in technical fields, who tend to be highly dedicated toward completing the program (if for no other reason, then because if they drop out of the program, then their student visa is voided and they have to go home). I'm sure there are other reasons as well.</p>
<p>Generally, those who don't complete the PhD will get a master's degree. Hence that's why you sometimes hear of the master's degree as a "consolation prize". Incidentally, that's also why you sometimes (not always, but sometimes) hear of master's degrees as having a bad connotation to them, especially from people who do have their PhD's, because they sometimes see a guy with a master's degree as somebody who tried to get his PhD, but wasn't good enough. One should note, however, that this attitude is certainly not a common one. However, you should know that that attitude is held by some people out there.</p>