There have been a couple of Y-DNA matches between descendants of Jeremiah Vail (b. ca. 1618, England?, d. 1687, Southold, Long Island) and James Fales (b. ca. 1630, England?, d. 1708, Dedham, MA). Y-DNA is passed on exclusively in the male line and is thus useful for tracing male-line descent. The haplogroup is I2a (formerly known as I1b).
Two descendants of Jeremiah Vail have matched each other, one descended through Jeremiah's son Jeremiah (results and pedigree available online at smgf.org; registration required) and the other through Jeremiah's son John (private communication to me).
These Jeremiah Vail results match those of two descendants of James Fales (results and pedigrees also at smgf.org) and two other Fales whose deeper ancestry is unknown; one is from Wilmington, North Carolina (both at ysearch.org). One of the James Fales descendants is through James' son James and the other through James' son Peter.
The fact that the matches are through separate sons of the immigrant ancestors is a good sign that the results are a valid reflection of the Y-DNA signature of the immigrants.
The strong possibility of a close relationship between the two families should be kept in mind by future researchers.