From previous (untested) research, I would recomend using a (-) over and
underscore (_). I've never thought of using + but I reckon it could have qwerky
results maybe to do with the fact that plus signs are used when searching quite
frequently.
Also, I think there may be problems with some old browsers reading urls with %20
so I wouldn't use them.
Haven't a clue about double spaces but personally I'd stear clear as I think it
would make it harder to read and just lengthen it for no particular
reason.
