I started my "bulking" phase back in November. I was 185lbs. As of this morning, I'm 205. 20lbs in 12 weeks works out to about 1.5 pounds per week. This seems to have been working nicely for me, as my BF% has gone up very little. I found in the beginning, I was averaging a 2-2.5lb per week gain, but was putting too much around the middle, so I cut it back a bit.
For me, this all translated into about a 500 cal per day increase in food intake. 3500 per day seems to be my "sweet spot" for putting on weight, 3000 seems to be my "maintenance". I must admit however, my gains have been slowing, so I'm figuring it's time to either up the cals again, or start trimming down SLOWLY for summer, hehe.