If you don't want to pay the extra, often downgrading the line to the business equivalent of the speed tier below what you are currently using on your residential package will net out a similar monthly fee.
They have better contention ratios on Business accounts and so you may even see faster speeds at that lower tier.
Also they have a thing where you can pay an extra $5 to get basic TV (local channels, weather channel public access etc...).
It works out to be cheaper than residential internet + basic channels.
We downgraded a 50Mbps Comcast line to a 25Mbps line and I honestly couldn't see much difference in terms of actual page load time, file download speeds etc but we saved some $
http://customer.comcast.com/Pages/FAQViewer.aspx?Guid=ce29df...
And plus, I don't buy the "Our networks can't handle the strain!" argument companies like Comcast keep bringing up. I mean, in the grand scheme of things, 250 GB of data isn't that much for a company the size of Comcast.
A correct solution would include a guaranteed increase in the cap yearly (at least) based on the rate of bandwidth usage inflation. I've used massively more bandwidth every year as things like streaming, HD video, etc. become commonplace.
If you break the cap twice there are no overage charges, they just disconnect you for a year, no matter what you're willing to pay. When they called me and said "use less or use nothing" and refused to suggest any way to let me pay for more of their product, that was extremely consumer hostile.
The only solution is the small business plans which are not capped, which they do not tell you about, but fortunately I found out about them in HN comments.