I think we were really lucky with DS1, maybe it was because he was that bit older, old enough to have things explained to him, but he hasn't had even a moment's of jealousy, he has just absolutely doted on DS2 since the moment he first saw him in hospital.
I think it helped a bit that with DS2 arriving in December, (rather than November when he was due!), DS1 had things going on for school (xmas parties, plays, fairs etc) and then we had family and friends visiting bringing pressies for them both, then of course xmas itself, it made that whole month absolutely chaos for us, but DS1 loved it! By the time xmas had died down, DS2 was part of us as a family, and DS1 could barely remember not having him with us.
I think this time we may see some more problems from DS2, DS1 will be fine, I've no doubts, but I think DS2 is going to be just a little too young to understand it all, he is suddenly going to be thrown in the deep end, with this baby that came out of no where.
He is quite loving towards other babies, giving them kisses and cuddles, but it is very different seeing a baby for a couple of hours, than it is having one move in with you! Who knows? He might take it all in his stride, he is no where near as sensitive as DS1 is, and he got through it!