You don't need to take time every day (or every few hours) to log in to the usage site, click through to the relevant page and grok the details; DataFox will give you the info you need instantly in your statusbar, additional information is available in the tooltip. Statusbar and tooltip strings are completely customizable.
The progress bar gives you an idea of the amount of bandwidth from your monthly limit already consumed. Color coding as as well as surplus bandwidth calculations let you know instantly whether you need to conserve bandwidth or whether you have loads to spare. If you're overlimit on a particular day, the progress bar will be orange with red text, normally it's cyan with black text.
DataFox currently supports two of the largest ISPs in India, BSNL and MTNL. More ISPs may be added in the future.
Visit the DataFox website http://thegoan.com/datafox
for further details and illustrations.