revisiting an older thread... I tie my belt the way I was shown by a bunch of yudansha in a judo dojo, and the way the guys at the Kodokan tied their belts when they trained on the Japanese national judo team (I watched - the only one that ever practiced with me "gave me a lesson" - it was fun, but a whole 'nother level). Everyone there, including Yasuhiro Yamashita (again, I watched) had their belts un-tie and trail behind them at some stage.
I've seen some aikido people tie their belts with a sort of basket weave, and it didn't come undone, and I've seen others loop their loose-ends around the belt again, but that wouldn't be permitted in judo, where your opponent's belt is sometimes used in newaza to control your opponent.
I've also seen people with a different type of belt from the standard judo-type belt - one in particular who's spent several years in Japan - his belt seems to taper and is tied quite differently, but I've never been told that my belt was tied "wrong."
They work loose. It seems to matter to Aikido people - I seem to recall the judo folks treated it as a minor inconvenience.
Is there a web site somewhere with "how to tie an obi so it won't work loose" video? Will have a look at youtube and report back.
Ok - found one. tried it - seems to work...