That whole shared connection argument is misleading. While its true that cable is sort of a "party line" set up, there is no real performance hit. In reality, the whole internet is a "party line" set up at some point. Cable just moves the sharing closer to the wall. But as long as the pipes are big enough, it shouldn't be an issue.
The typical downstream performance of cable blows the doors off of dsl. Most cable users see 2.5-4 Mbps down and usually 256kbps up. Compare that to an average of 768kbps for dsl. Cable is basically 3-5 times faster than dsl downstream. There's a reason cable modems are hugely more popular than dsl.
I suppose security is somewhat of an issue, but its basically the same if you have a router and firewall set up. I guess someone could sniff packets locally, but most of your important internet traffic(credit cards, passwords) are (hopefully) encrypted anyway. Besides, if you have a mac, your already protected against a lot of things.
As far as I can tell, the only reason to get dsl is if cable is unavailable or if you need the higher upstream of dsl. Even so, most cable companies will uncap the upstream for additional cost.
