You are able to upload workout information from a long list of training devices, and that list is growing daily. The log supports many devices from Garmin, Polar, SRM, CycleOps (Power Tap), Quarq, Timex, RacerMate (Computrainer) and Tacx to name a few.
The log is provided and maintained by TrainingPeaks. A full list of the supported devices can be found on their site here: http://support.trainingpeaks.com/compatible-devices.aspx