As Flik's post implies,
when it comes to tallying the various types one has flown, only solo time is truly meaningful. IMHO, riding along as a student, observer, passenger, or "PIC under supervision" (talk about an oxymoron!) just doesn't rate.
Cecil Lewis said it best:
Flying alone! Nothing gives such a sense of mastery over time over mechanism, mastery indeed over space, time, and life itself, as this.
P.S. The above is not meant to imply that dual time is worthless for the purpose of assessing someone's piloting skills. At least in my experience, one hour of dual given by a good instructor can sharpen one's skills better than ten hours of solo practice.