Depends what you want from a 'walk round'. I've got one on a 5D and its a great lens for macro and portraits. However, on a 400D it would be like a 160 mm on a full frame. This is very long for a general purpose lens but without know what you're hoping to shoot it's hard to advise. If it's candids you're after it could be ok as you can shoot at distance.....
I guess the other question would be what other lenses do you have and why are you looking to get this lens and use it in this way?