After a while this thread gets tedious to check in on, cause it's the same questions over and over again. So I'm gonna sum it up in a single post, which may make it easier to re-post when the need arises (if I miss anything let me know and I'll edit it):
What we know about B.O.B's:
1. Stand's for Born On Board a reference to Bungie's game Marathon.
2. The spawn on every level in campaign with exception to Noble Actual. Though on Exodus and New Alexandria only BOBshee's have been found. (B.O.B's in Banshee's)
3. They currently unlock nothing and as far as we know are just an Easter Egg reference to Bungie's Marathon.
4. They give you a medal when you kill them that is only available on Bungie.net
5. They spawn in the same area's based on the game timer, or the proximity, or do to some special event.
6. They are ALWAYS Elites
7. They are Almost always Gold Ranger Class Elites
8. The exception is on ONI: Sword Base where they are white with randomly generated armor.
9. Any rank Elite can be a B.O.B
10. They are extra tough and harder to kill than normal Elites.
GRD/B.O.B Helmet
1. IT IS NOT ON THE Halo: Reach DISK this has been proven.
2. It is not known if it will ever come to console.
3. Bungie blue flames, the legendary flames, Elite Officer Armor, all came pre-shipped on the disk, which means that they have always been their and were not added later on. This means that GRD/B.O.B Will not be added by Bungie later on.
4. It is unknown if 343i have the ability to add armor to Reach, only theories have been proposed no confirmed information.
5. GRD IS B.O.B
6. GRD comes from people who have claimed to see the helmet in Tender Loins armory during Bungie Day 7/7/2011, it is unknown whether this is its actual name. Although Bungie has stated that it was not actually in the armory and that people only thought they saw it, when in fact they didn't. Some people take this claim as false do to Bungie's history of keeping things secret.
7. The reason it's called B.O.B is because of the way it looks, which is similar to the B.O.B's of Bungie's Marathon.
8. No you can't unlock it.
9. The only confirmed images of the helmet is from IGN's preview/article on the Defiant Map Pack developed by Certain Affinity and published by 343 Industries. This same picture was featured on the Xbox Live Dashboard.
10. I cannot stress enough IT IS NOT ON THE Halo: Reach DISK!
[Edited on 07.31.2011 8:15 PM PDT]