We picked up are stick last year at the TelCel office in Guaymas for around 430 pesos for 5GB for 60 days. The plans seem to change all the time and the office may have different plans than what is shown online. As far as I know you can only get the Banda Ancha at real TelCel offices but not at the franchise stores where they only have phones. It worked almost everywhere but is not consistent speed-wise.
To know how much you have used there are places to click - toward the upper right is a clicky that says INTERNET CONNECTION RECORDS - if you click it will show you how much you have used - if you click CLEAR it will clear the records and you won't know how much you have really used - but of course it seems like it sometimes resets itself - I think you can check your time online but I forget how and we are back in the US so can't do it.
The software that comes with the stick is not accurate for checking usage.
Online you can check your usage, money balance, add fund to your account, activate your monthly usage and transfer funds to another telcel number. You also have an email address and can access it here too. Just use the link above in my other post and register. It is in Spanish but not to hard to follow.
If you have the Google Toolbar with Google Translate you can just click to translate and see most of the webpage playaboy reference above in English so it is not to hard to navigate. You have to sign in and create a password and then you can access everything you want to know about your account.