Yes, I have considered this, but haven't messed with it just yet. I drop the priority for the dedicated cores I put to it, but haven't messed with running both a GPU and a CPU associated with the same core with the minerd at lower priority.
It works just fine. No need to mess with assigning cores to threads. There is no bitcoin mining performance impact on my rigs from running litecoin miner.
I may fiddle with it eventually, but it's only 6 cores that I have right now. Not too much I'm leaving on the table given CPU chain value ATM.
No fortunes no, but I mine about 1000 LTC per month with 2 rigs. For now at least, thats a bitcoin or two. Still nice.
If you are realling mining a bitcoin or two per month, is it not better to give up? You are wasting more electricity than you are earning money...