The big claim of cable internet access over services such as DSL is the faster download speed (DSL is often limited to between 512kbps and 1mbps, whereas many cable providers have 1.5-3.0mbps maximums). Security Focus is carrying an Associated Press article that discusses recent moves by Comcast to limit users downloads and may be pushing high-volume users to the phone company.
This is not the first time that this issue has come up. With growing regularity over the last few months, complaints have been coming in about cable providers sending letters to their consumers alerting them that they are in violation of the Acceptable Use Policy (AUP) governing the use of the service and telling them that if they don't cut their usage to acceptable levels, they will be ejected from the service. In a manner befitting the IRS, the folks at Comcast neither mention said AUP in their description of service, nor do they define the specifics of how much bandwidth is too much.
When pressed by AP for specifics, they gave none.
DSL providers have been having a hay-day with this, inviting abused users to their services and strongly stating that they don't now, nor will they in the future limit people's use beyond the limitations built into DSL.
For the Cable providers, this provides a bit of a problem, since they have no good throttling mechanism as the DSL providers do. On the DSL side of the fence, you can purchase personal DSL, which is fast for downloads (usually up to 768kbps), and slow for uploads (often as little as 128kbps), and usually multiple forms of "enterprise" DSL, which have varying levels of speed, up to 1.5mbps download and at least 768kbps upload.
Another difficulty for the cable folks is that they share bandwidth very early between customers. Thus, if your neighborhood has 300 homes and everybody's cable modem is limiting individual use to 1.5-3.0mbps, you can expect in worst case situations for the bandwidth demands to approach 300mbps. It's highly unlikely that there's that much bandwidth into your area, since it is way above the average expectations. So, consider that the cable company runs the equivalent of a DS3 into the area (45mbps), you're still looking at 150kbps per user. About 5x the dial-up speed, still, but not nearly 1.5-3.0mbps.
DSL, on the other hand has two advantages in this situation. First is that they don't share until they reach the CO (Central Office). Next, it isn't out of the ordinary for a CO to handle literally thousands of lines. They may not all have DSL, but the efficiency of ganging the lines together and being able to leverage capacity spikes across more customers, while also limiting customers on a per-user basis give the telcos a great deal of flexibility.
Not surprisingly, there exists what looks to be a predictability vs. speed issue going on between the cable and DSL providers, with cable providing fastest spot speeds, and DSL providing consistency.
Of course, even those issues don't matter if either service is lossy.
In the end of the day, I think we'll see a continued fight between these two delivery mechanisms, especially as more businesses and home businesses take to using them. Price and quality will be at the center of gaining customers, but customer service, as usual will be at the center of losing them. If the cable providers continue to push for "easy" customers, then they will eventually have trouble keeping the early adopters, who are the ones that govern where their friends and associates will go.