as u can see im from brazil
here Jiujitsu is very popular. we've got the famou brazilian jiu jitsu. belive me, heaps people here do Jiu jitsu.

if u want to know if jiujitsu is effective in street fight i'd say NO.
ive seen some fights against JJ, and most of then they loose. why?
because u dont take a street fight to the floor like that. u cant roll on the floor and wait to do your arm lock.
in street fights, most of time u arent alone. people wouldnt just watch u get bashed on the floor.
another thing, is too hard to take u to the floor if u r good praticer of tkd, mt or kung fu. they came to take u down with their head down, easy to kick their heads.
if u still like JJ, keep doing it BUT if u r looking for street fights, start to do a stand up fight, id recomend muay thai, because muay thai and jj together is a good combination.