But today, a comment from a reader on an old, old post raises an interesting question that I'm not sure how to answer, so I thought I'd ask my readers -- if, indeed, any of you are reading. If today is hir deadline, chances are that the answers may come too late to do much good, but I'd like to hear what others think -- especially those of you who are at institutions with doctoral programs.
What are the unspoken rules about accepting a PhD program and backing out last minute? I got offered a position at a University which wasn't my first choice; I am afraid to walk away and I wanted to accept and let them know for sure closer to when the program starts. How bad would that be for my career?
As longtime readers know, my institution doesn't have a doctoral program, so I can only guess at the answer to this question. What I have below are off-the-cuff thoughts, not to be relied upon. Hopefully more experience readers will chime in.
(a) Would it be unheard-of? No. If you backed out, you wouldn't be the first person to do so. Things happen between April and September: Illnesses, financial catastrophes, family emergencies. And yes, some people simply get offers they can't refuse.
(b) Would it be bad for your career? That all depends on the faculty at the institution you're at. If they're grudge-holders with some influence in the field, then yes. If not, then probably not. And it may be that if and when the day arrives that you enter the job market, they will have forgotten all about some aspiring grad student they never met.
(c) Would it be inconsiderate? Well, maybe a little. Programs have limited places. If they're offering you one, there is likely some other applicant out there in the cold (or accepted by a less-preferred school when your suitor is their preference). Same goes double if your suitor has offered you a funding package. If you're in the sciences, advisers may have to make calculations way in advance as to how they're building their lab teams -- I don't know anything about that, personally, but it may be a more serious issue. If you back out down the road, it may be that the offer and/or funding can go to someone else. Or maybe not. But this brings me to a related point: The aspirant suggest that s/he might "accept and then let them know for sure closer to when the program starts." If I'm reading that right, that won't fly. You either accept or decline. There's no seat-saving in grad programs. And you'll also want to read the conditions of acceptance carefully: I've never seen contract-type language in an offer that specifies consequences for changing your mind, but if there's a financial offer in there then there just might be. If that's the case, then you want to tread more cautiously, because you may be signing something legally binding. Again, I've never seen such a thing, but it's been a long time.
(d) Is it a moot point? Perhaps. I'm trying to think of a situation where one school has their April deadline and another you haven't even heard from yet. There are only two: (1) you're wait-listed at Dream School and they've informed you of such; (2) the program you're waiting to hear from has a different notification calendar, so nobody's heard. If neither of those two obtains, then I think it's a fairly safe bet that the call isn't going to come, and there's no sense waiting for it.
Here's my thought: all academics should strive to be courteous and professionally considerate in all things. This includes not stringing along potential advisers and allies. On the other hand, all academics balance this with their own best interests, and sometimes this has professional consequences. Were it me, I'd accept the bird-in-the-hand offer, unless it were somewhere I really, really didn't want to be. And if Dream School came knocking later, I'd scrutinize that offer very closely and ask myself whether accepting it would be worth whatever consequences came my way -- remember that you don't have to accept an offer just because you have one, and the "safety" school may in fact turn out to be a better fit than the high-profile one you were aiming for.
That's my two cents. Again, pulled straight out of my nether regions, as is almost all my advice. So I defer to my six remaining readers: What would you tell a person in this situation?
 At least it was back in my day. But that day was a long, long time ago.
 Like that's ever stopped me.