Is there a network usage utility that shows data usage by network connection I use my Mountain Lion MacBook Air to connect to the internet using various methods. At home, I use my wired connection, which does not have a cap. Sometimes though, I connect via my iPad, which uses LTE, and does have a bandwidth cap. At other times, I connect through 3G on my iPhone, where the bandwidth cap is even lower.

Is there a utility which would run on my computer and automatically track and record the amount of data sent. I am interested in seeing the data by connection (which WiFi network I connect to) and be aggregatable by date (so I can see for today only, month-to-date, previous month, etc). For example, I would like to be able to see how many megabytes of bandwidth I have used in March 2013 while connected to a WiFi network called "Bob's LTE" or May 1st through May 8th 2013  while connected to "Bob's iPhone".

Does such a beastie exist?
If you are looking for simple real time statistics, checkout iStat Pro. 
It is a widget that provides a lot more than just network information.

http://www.apple.com/downloads/dashboard/status/istatpro.html

Surplus Meter or Net Monitor look like they would do exactly what you want:

http://mac.appstorm.net/roundups/internet-roundup/4-ways-to-monitor-bandwidth-usage-on-your-mac/