I have different regimes for each dog. As Revel has aged, he has developed a greasier coat which is particuarly noticable when he is moulting. I would probably do him between 4-6 times a year. If he is being shown at a major show (rarely now) he gets a bath a week to 10 days before which allows the coat to 'recover' but not (hopefully) get dirty. After bathing for a few days the hair is soft and silky and not the correct texture for a sheltie which should be harsher - hence the recovery period. Always before a show I wash the white areas, legs, chest and tummy etc and I have a special 'blue' shampoo for whites which I save for Crufts as it is rather pricey! It always sounds like I'm doing the laundry when I say I'm going to "wash the whites!"
Epic, the younger tri boy is a dirt magnet! I'm sure he was born to be a working dog as he is forever plastered in mud and where the other shelties will skirt round a puddle, Epic ploughs straight through! However, because he is younger he doesn't have the greasy coat issues that Revel has so generally I just clean the dirt off as best I can with a bowl of water for feet and cloth and let the rest drop or get brushed off when dry.
Now I am going to horrify everyone and admit that Yogi has probably only had about five baths in his entire life!

He last was bathed after his operation about March 2011!

He has the same feet and whites cleaning as the others but he has the most amazing coat which never seems to get dirty. When I did bath him, it was the first time in about two years and the water came off almost clean! He has amazing skin and no doggy smell and when in coat, it is massive. His coat always feels clean to touch as well. I guess he is just one of those natural dogs. He has what I would describe as a dry coat where as the tris are more oily.
Of shelties in general, I've noticed that sables seem to shed more hair than tris for some reason - either that or the tri-colour hair is less noticable...
Because we live in a rural area they mostly only encounter 'clean' dirt which probably helps as does natural washing when they go out in the rain. They are brushed usually once a week which is a 'deep brushing' and takes about an hour per dog. They lay on their sides on the grooming table so often fall asleep - apart from Epic who hasn't mastered that yet. Trimming is generally when necessary, always a week to 10 days before a show but for maintainance when I notice it needs doing and I hate shaggy feet so tend to keep quite on top of this. Epic and Revel hardly ever need their back feet nails cutting and not much off the front ones either but Yogi has always had long quicks which makes keeping his feet looking decent difficult as he has naturally long nails.
I have heard that frequent bathing can actually make shelties shed more and factors like central heating etc can make it worse. Some foods I think can also be a contributory factor. I have used a product called Yumega (for Revel) which seems to help with a healthy coat but I don't know whether it is sold in the States. Cod liver oil/fish oil products might help reduce excessive shedding too.