I just picked this up and am blown away. Next best thing to private lessons for the price of one or two of them. Can use a mic and the program will tell you if you are on key. Can play with or without backing, metronome, change tempo as needed. I can't vouch for it personally, but eMedia claims if you master all of the lessions, you will be a bass player and can climb on stage with other musicians and hold your own. I would imagine it takes a bit long to become a virtuoso however (read never for some of us)
http://www.amazon.com/eMedia-Bass-Method-V-2/dp/B004TQQWSA/ref=pd_cp_sw_0
http://www.amazon.com/eMedia-Bass-Method-V-2/dp/B004TQQWSA/ref=pd_cp_sw_0