I've been experimenting with this for a little while now and would be interested in the experience of others. For me, I normally tie a very short bimimi double to attach to a twisted leader. I in fact try to make this segment as short as I can and this is usually about six inches in length.
When tying bimimis quickly however, I have found it much easier to tie a long doubled section. This is using the method whereby you loop it first around your feet and then around your knees. By spreading your knees, you automatically do the wind back section so you can then finish it with half hitches or a rizzuto (thank Mark) as I learned yesterday. I can tie one of these within a couple of minutes whereas a short bimimi (assuming 50 - 70 turns) takes me five minutes as it is very hard to do it this way. The reason why is that I have to manually wind back a short bimimi by hand.
The problem with a long doubled section is that I believe it increases the possibility of the loop catching on the guides (especially the first guide) when you're casting. With a short bimimi, I very rarely have wind knots (and can I say that the terms should be "wind' as in "winding", not what causes a breeze) whereas I have found that with the long bimimi, I definitely get more wind knots.
Interested on the observations of others.......