Souljourner makes some good points, but I'd also like to add to them.
There is a very good reason that a group of spotters has a good chance of finding a group of hiders (especially if those hiders are moving around). Why do you think scouts go out one at a time, rather than in huge groups? Or that thieves...burglars and such, or at least the ones that rely on not being seen (as opposed to the ones that wait until the place is empty and just break in)...go in alone, rather than in huge groups? It's a whole lot easier to spot multiple people, and even if all of the members of the group are skilled, there are often only so many hiding places, or someone will make a mistake, or it will be easier to see the mass of moving things rather than the one small moving thing, and so on. And of course, when you're talking about people who have absolutely no idea how to hide (i.e. the fighter with no ranks in it, and a low dex and wearing full plate), then this problem gets even worse. This happens a lot in my party, where I am often the one to play the rogue...I usually try to go ahead alone (sometimes everyone else decides to come with, ruining the idea) because there is too much liability associated with being a large (or even small) group trying to hide from people whose sole purpose is to find you. So it should be nigh impossible for a group to hide from a group of spotters in most cases (for ambush-type situations, however, it's sometimes advantageous to have multiple hiders, because then there can be communication between all the various hiders in order to find the best hiding spots and such, and they can point out each others mistakes...but this only applies to when the hiders are staying put and finding very good hiding places and such...I would probably treat it like the take 20 idea that was brought up earlier, or maybe give a hefty circumstance bonus for good hiding places)
There is a very good reason that a group of spotters has a good chance of finding a group of hiders (especially if those hiders are moving around). Why do you think scouts go out one at a time, rather than in huge groups? Or that thieves...burglars and such, or at least the ones that rely on not being seen (as opposed to the ones that wait until the place is empty and just break in)...go in alone, rather than in huge groups? It's a whole lot easier to spot multiple people, and even if all of the members of the group are skilled, there are often only so many hiding places, or someone will make a mistake, or it will be easier to see the mass of moving things rather than the one small moving thing, and so on. And of course, when you're talking about people who have absolutely no idea how to hide (i.e. the fighter with no ranks in it, and a low dex and wearing full plate), then this problem gets even worse. This happens a lot in my party, where I am often the one to play the rogue...I usually try to go ahead alone (sometimes everyone else decides to come with, ruining the idea) because there is too much liability associated with being a large (or even small) group trying to hide from people whose sole purpose is to find you. So it should be nigh impossible for a group to hide from a group of spotters in most cases (for ambush-type situations, however, it's sometimes advantageous to have multiple hiders, because then there can be communication between all the various hiders in order to find the best hiding spots and such, and they can point out each others mistakes...but this only applies to when the hiders are staying put and finding very good hiding places and such...I would probably treat it like the take 20 idea that was brought up earlier, or maybe give a hefty circumstance bonus for good hiding places)