I know Frumby's gonna light up his flamethrower on this one, so I'm gonna jab first!
Actually, I don't think you can say flat out that any general differences exist, because DI's (regardless of what kind of camo soft cap they wore before having the "smoky bear" grafted to their heads), regardless of what they've been told to do, teach more or less according to their personal beliefs in the military based on their own experience. Some are screamers and some aren't, period. Some stress the academics from day 1 and are laid back, while others believe that there is no substitute for experience (which you'll get later on, hopefully) and likewise spend 90% of boot drilling you on the basics, and only familiarizing you with what's required in the smartbook.
My boot was OSUT (One Station Unit Training) and was 13 weeks with no follow on advanced. We had 6 platoons, 2 DI's each, all in one building and throughout the course of that you saw a lot of the other DI's, who gave instruction for everyone, and you saw a lot of different styles!
When you show up for Boot you're going to be standing in a line and hearing a, loud, carefully prepared speech from your DI that includes all the stuff the Army wants you to hear on day one. However, four weeks later, when your all standing around a fire-in-a- drum, on some godforsaken range under some abysmal weather at 3:30 in the morning, and the comedian side of your DI comes out, that's when your gonna hear how it really is when you get out to a unit.
Take the show BOOTCAMP for example, all real ex-Marine DI's (who are now no doubt trying to jumpstart acting careers) but you can see that the 4 of them have different styles of doing things. Some will seem like big brothers, others will be like school yard bully's. Also think from their point of view: different behavior on their part is required to get performance and results from different recruits/OC's. Some will need more screaming/push-ups/etc, than others to get the point. Their there to teach and that's the bottom line, whatever gets the job done. If you do get stuck with a screamer who seems to have it in for you and only you, just rest assured that he wouldn't be there if he didn't know what he were doing.
My $0.04
D