To elaborate on the damage of the DL stints to Cubs starters:
When the original 5 start the Cubs are 19-14.
When the replacements start the Cubs are 3-12.
I think it's probable to say the Cubs would be sitting better than .500 right now if they hadn't lost their pitchers.
Even losing only one pitcher and using Silva would have probably been enough to keep the Cubs over .500. Jay Jackson might have also been able to make contributions but he has battled his own share of injuries this year. These are the breaks.
Also on the Horizon, Kenneth Trey McNutt, could be a contributor by the end of this season. I use all three names because I'm not sure what name he goes by. He's probably better than Casey Coleman right now but still in Double-A, performing solidly but not spectacularly.