I've just finished up a 3 week prop cycle 100mgs eod. Last shot was last friday. I gained 10 lbs in those three weeks and have gained 2lbs this week during avena/tribulus/nettle/maca/proviron PCT. I'm sure the same would apply for a dbol cycle just depends on how hard you train and eat on and post cycle.
Nope, no sides. The three week thing is not for everyone but all I can say is give it a try. I know I definately will be doing another on in about 8-10 weeks along with IGF-1.
poantrex is right, some people do have a hard time keeping gains from dbol only. I personally recomend test prop but if you do the dbol only cycle keep your calories up post cycle and don't slack off and you should do fine.