comcast offers 'up to' 12mb/s and 'up to' 14 mb/s, and there's a current promotion which supposedly 'doubled' that speed in our area (jacksonville, FL, US)
my current speed tests show about 15~16 mb/s download speeds, and 6~7 mb/s upload speeds... but these are much better than usual, for this household.
Comcast is horrible about cutting back bandwith depending on the usage, despite paying a flat monthly rate (just internet and tv for us, no phone). For instance, on some days i can be playing xbox live with absolutely no problems, then a few hours later i will start having host connection problems, terrible lag, and eventually be unable to connect. I hear the same thing from my friends who also subscribe under comcast here.
NOW TO CORRECT YOUR ARGUMENTATIVE MATH~~~
100/100 (redundant) also known as simply 100 MBPS which is exactly equal to 12.5 MB/s
our internet is measured in MB/s, yours mbit or mbps (same thing, different abbreviation)
the address below gives you a nifty little comparison bar and then values as to what that equals in different scales/units.
source:
http://web.forret.com/tools/bandwidth.asp?speed=100&unit=Mbps&title=100+Mbit+[Unmetered+Server]