The only thing I like about interleague is the rivalries between AL and NL teams with close proximity. Oakland VS SanFrancisco, Cubs VS WhiteSox, Mets VS Yankees, a stretch Marlins VS DevilRays...snicker
, Indians VS Reds, and a few others are great for the fans.
From a scheduleing perspective, I think it hurts the competetive balance of the season overall, but not too big a price to pay.
"Son we would like to keep you around here but were trying to win a pennant this year."