I would estimate that the practical speed of Centurylink's cheapest DSL speed is too often 125Kbps. Let's compare that to Comcast's cheapest cable speed of 10Mbps. I used a calculator, and found that Comcast's cheapest plan is 80 times faster than Centurylink's cheapest plan. For reference, dial-up had a practical top speed of 53Kbps.
The problem with this is that your computer can't properly access the Internet or do updates with speeds as slow as Centurylink's. Current Websites have images, videos, ads, and plugins that require about 10 times the speed that the cheapest Centurylink plan offers. In addition, the primary way to keep your computer safe from malware is to update Windows, anti-virus, and many other programs on your computer.
So, if Centurylink is your ISP, I suggest either switching to a cable Internet provider (such as Comcast) or upgrading your plan. The extra cost may be $20/month for Centurylink's better plan.
Now, how do I know Centurylink is too often slow? I will admit my research is anecdotal. Take a look at the screenshot above. The primary thing that Google thinks your are searching for when you type in "Centurylink is" happens to be "slow," not "down," "bad," or "owned by such and such." Also, during my tech support travels I have never once found Centurylink's cheapest speed to be satisfactory for use, especially in the suburbs.
I care about my customers, and I hate to see them with invalid Internet service.