When I have the information I record miles, whether on the bike or on a run. However, I keep track of time for each activity as well and compile that for a weekly total. The weekly total in time is most important to me because it includes every activity. I can look back in my log books prior to an event and see how much time I was putting in and how it positively or negatively affected the outcome. If you only look at miles and ignore the other time put in (even time lifting weights or yoga) you may cross the line into "over training" before you realize it.
I am a bit like Jenny though, and record data on anything that I can! Heart rate, average pace etc... sometimes it's nice to leave behind all of the gadgets and just go out for a run - even without a watch!