The Vulocity automatic mileage logger logs your commuting and business miles while driving your personal vehicle. Keeping a log book by hand for tax purposes is a pain. To have a gadget take care of the paper work is exciting promise.

The Vulocity gadget calculates the mileage using GPS technology and complete trip information is sent to the Vulocity web solution over cell networks. No software or other special items are required.
You can access your data from any computer with internet access. Each start/stop session has a separate record with date, time, location, miles traveled and the time duration. Store comments about individual records and export your records into Excel or PDF formats.

On the one hand it is convenient to just leave the GPS logger in the car and have not to deal with downloading data to a PC. On the other hand there is some privacy concern as the company is keeping track of where you are driving all day.
The Vulocity Mileage Logger sells for $329.90 on their site.