Same here. I don't want to have too much fiat or else I'll be losing out on the rising BTC price (Making $20 off arb isn't so great when you could have just kept that cash as btc and cashed out when they are each worth $20 more). Mt. Gox and Bitstamp need to swing back and forth to create an optimal system, but Gox has been constantly charging ahead lately...
Yeah, I used to tell my bot to have half in fiat and half in BTC but as the price kept going up (this is from about $6 to $12 last year) I just saw the number of BTC I held going down. That was getting depressing so I changed to having a target BTC holding instead. I'm glad I made that change.