I think standing is an important thing to do on long rides. It seems to me that regardless of how good your saddle is, being seated anywhere for prolonged periods of time, reduces circulation. Even when working in the office in front of my computer, I make it a point to get up once and a while. On a typical ride I'll stand when going over a rough patch of road, while climbing (however, I remain seated more on long climbs), and once every now and again, I'll shift to the big ring and smallest cog and stand sprinting for a few hundred yards (in part to work different muscle groups).