i was honestly thinking about doing it wheni was gonna buy a cbr. i think it looks cool, a buddy of mine has a slight extension like 6" and lowered a bit and his bike looks badass.
i think it prolly depends on what you buy your bike for. if both ends are lowered the exact same then it wont adversly affect your handling characteristics, you just might not be able to knee drag (like most riders do that anyway)
an extended swingarm can through off your handling and it will be like learning to ride a new bike, but honestly if all you do is ride the bike around town then what does it matter.
like me, id ride to work and back and thats about it, 20 maybe 30 miles a week. im not trying to be a gp racer in town, i dont give a shit about stunting, im not gonna be hitting twisties on the weekends, any of that bullshit.so honestly it wouldnt bother me at all.
hell if anything an extended swingarm will keep your front tire on the ground, which is a good thing
it seems like the squids like this sort of stuff and the "real riders" dont, but to me honestly it just depends on the person and how they ride.