Interesting emerging observational properties of the period-mass distribution of extra-solar planets are discussed .
New recent detections confirm the already emphasized lack of massive planets ( m _ { 2 } \sin { i } \geq 2 M _ { Jup } ) on short-period orbits ( P \leq 100 days ) .
Furthermore , we point out i ) a shortage of planets in the 10–100 day period range as well as ii ) a lack of light planets ( m _ { 2 } \sin { i } \leq 0.75 M _ { Jup } ) on orbits with periods larger than \sim 100 days .
The latter feature is shown not to be due to small-number statistics with Monte-Carlo simulations .
These observational period-related characteristics are discussed in the context of the migration process of exoplanets .
They are found to be in agreement with recent simulations of planet interactions with viscous disks .
The observed valley at a few tens of days in the period distribution is interpreted as a transition region between two categories of planets that suffered different migration scenarios .
The lack of light planets on longer-period orbits and the corresponding intriguing sharp limit in mass is tentatively explained by the runaway migration process recently studied by Masset & Papaloizou ( 2003 ) .
The observed properties also have implications for the observation strategies of the on-going surveys and of future higher-precision searches .