I used to have dreads for a few years, then I cut them off about a year and a half ago, and now I think I'm gonna grow them again! At least two people have now said I looked better with them...
WRT headlice, you don't necessarily need to shave your dreads off if you get lice, you just need the right stuff to kill them. Most headlice remedies have insecticides that stay in your hair forever that kill the lice, and then you have to use a fine tooth comb to get rid of the eggs (obviously not possible with dreads!). A better way is to use larkspur and ascetic acid/white vinegar like they used to use in World War I in the trenches - the larkspur kills the live lice and the vinegar kills the eggs. It's sold as 'delacet', most shops don't stock it but Boots ordered it and had it the same day (must have stocks in their warehouse, it is available on prescription too so I guess they have to have it to hand) when I needed it. Worked perfectly for me first time and my dreads remained intact.