A PubMed search revealed this recent work:
Contagious yawning: the role of self-awareness and mental state attribution
Platek SM, Critton SR, Myers TE, Gallup GG.
Brain Res Cogn Brain Res. 2003 Jul;17(2):223-7.
Contagious yawning is a common, but poorly understood phenomenon. We hypothesized that contagious yawning is part of a more general phenomenon known as mental state attribution (i.e. the ability to inferentially model the mental states of others). To test this hypothesis we compared susceptibility to contagiously yawn with performance on a self-face recognition task, several theory of mind stories, and on a measure of schizotypal personality traits. Consistent with the hypothesis, susceptibility to contagiously yawn was positively related to performance on self-face recognition and faux pas theory of mind stories, and negatively related to schizotypal personality traits. These data suggest that contagious yawning may be associated with empathic aspects of mental state attribution and are negatively affected by increases in schizotypal personality traits much like other self-processing related tasks.
Yearning to yawn: the neural basis of contagious yawning
Schurmann M, Hesse MD, Stephan KE, Saarela M, Zilles K, Hari R, Fink GR.
Neuroimage. 2005 Feb 15;24(4):1260-4.
Yawning is contagious: Watching another person yawn may trigger us to do the same. Here we studied brain activation with functional magnetic resonance imaging (fMRI) while subjects watched videotaped yawns. Significant increases in the blood oxygen level dependent (BOLD) signal, specific to yawn viewing as contrasted to viewing non-nameable mouth movements, were observed in the right posterior superior temporal sulcus (STS) and bilaterally in the anterior STS, in agreement with the high affinity of STS to social cues. However, no additional yawn-specific activation was observed in Broca's area, the core region of the human mirror-neuron system (MNS) that matches action observation and execution. Thus, activation associated with viewing another person yawn seems to circumvent the essential parts of the MNS, in line with the nature of contagious yawns as automatically released behavioural acts-rather than truly imitated motor patterns that would require detailed action understanding. The subjects' self-reported tendency to yawn covaried negatively with activation of the left periamygdalar region, suggesting a connection between yawn contagiousness and amygdalar activation.
I'm at home without full-text access to these articles, and IANAP, but what I gleaned from these abstracts was
1. Contagious yawning may require an ability to empathize with the other yawner's mental/emotional state
2. ... but it is not a specific mimicry response (the way one mimics another's hand gestures and posture while on a date?)
3. It may be a hard-coded behavioural response specific to yawning?
Like I said, I am not a psychologist, and those last two are pretty shaky but that's what I understood. I was unable to find any information on "dating mimicry" on the web either, it's just something I heard once.
This news story (external - login to view)
may be more helpful, though I was unable to find the published study (by Baenninger) referred to.