Let me add my two cents worth:

Another issue to consider is that the 3DGS network currently will send updates to everyone on the server... everyone... you cannot natively select who 3DGS auto-updates and who it doesn't (an update "fixing" this is in the works but don't hold your breath for it coming out soon).

So this means that if you are on one side of the map and another person is on the other side of the map, under 3DGS protocol, you EACH still get each others update even though you don't need each others information.

Imagine therefore that 25 clients recieve a 10 byte update. This means each client receives a (25 x 10 = 250B) update, their own and 24 others. Now consider that total bandwidth, that's (25 x 250B =6250B). That's 6.25KB even if you don't need to know what the other 24 people are doing.

Now, you can turn off the auto-update and program the update behavior yourself (this is what I do), but that's pretty advanced stuff.

So if you want to do a small (less than 10 people) MP game, use 3DGS' auto-update. If you want to do something approximating a MMOG, disable auto-update and program you're own routing (keeping in mind what giorgi said).