When merging data from multiple devices, there are frequently alignment issues for me. I have a garmin 920XT, and a wired (LYC) PowerTap. Since the LYC PowerTap time codes are relative to the start of the log, there is frequently "drift" between it and the Garmin. For continuous effort rides, this isn't much of a big deal. But, for interval efforts, it becomes a pain to assess HR/power relationships.

It would be nice to have a editor of some sort to shift/stretch the merged device files in order to align the critical portions of a workout.

Similarly, for devices that have overlapping data (speed, HR, etc) it would be nice to be able to set the priority/select the desired source. I always prefer to use the Garmin for HR...but, sometimes the PowerTap records some "noise" as HR data, and TP.com seems to use the Power HR data in those cases. I end up having to manually edit the PowerTap CSV file to "zero" the HR column so that automerge uses the garmin HR data instead.