When I used dial up which was only 15+ mths ago, I only had one slot open for uplds, but if I was away from the computer sometimes I would open 2 slots (but just occasionally ... obviously one slot is better except when you take in account for shared downlding from multiple hosts.)
My advice for p2p sharing nowadays ... get another HDD be that internal or external. I have 2 internals (120 GB each), a 160 & 250 GB external (though I don't use the 250 for sharing ... only for backup.)
External drives are getting cheaper by the day. Even if it's less than 100 GB, it's going to be cheapish. Be it USB or firewire connection. It doesn't matter. You'll be surprised how much happier you feel with the extra space & options for both backup & sharing. Most people who use DC hubs have external drives ... it's a fact of life for p2p nowadays. Perhaps some of the newish peers can learn from this concept/suggestion.
I know of some people who have mutliple 250 GB external drives set up for both downlding & sharing. Some specfically for uploading. (Yes 1-2,000 GB / 1-2 Terabyte shares)