Current definitions of Modern and Contemporary Blues

These are quotes from Allmusic.com -

Modern Acoustic Blues finds contemporary artists reviving the older, more country-derived styles of blues in its myriad strains. The form places a great deal of emphasis on instrumental expertise, providing the genre with some astounding players who do more than merely replicate older styles. An outgrowth of the folk music boom and original blues revival of the mid-'60s, its emotional makeup can encompass everything from provincialism to intense personal statements. While clearly honoring traditional forms, the style also has room for original material, providing a forum for new ideas as well as extending the genre's musical repertoire into the future.

Contemporary Blues draws upon traditional acoustic and electric blues, but offers a more smoothed-out take on the genre that incorporates the influences of rock, pop, R&B, and/or folk. As such, contemporary blues is most often (though not always) electric, and rarely (though once in a while) purist. Because of its up-to-date production and mellower audience sensibility, the style tends to be more polished and sometimes even a bit genteel; it's still definitely soulful, but not quite as earthy or gritty as the music that predates it, and not as aggressive or fiery as modern-day electric blues from Chicago or Texas. Since it's informed by other types of music, contemporary blues has a greater chance of crossing over to pop, album rock, or adult-contemporary radio formats. Artists like Robert Cray, Keb' Mo', and prodigies Kenny Wayne Shepherd and Jonny Lang epitomize the contemporary blues sound.

I think these are pretty good definitions. Well written too!