It seems to me that the SB (Spirit Bomb) can only take energy outta things that will it, at least for the intelligent stuff. With things like Rivers and animals, it could be they have no will to resist it, or that they instinctively like and trust the pure-hearted Goku.
Frieza & Buu Saga Spoilers
Anyway, in the Frieza saga there was NO indication that creating a SB weakened Frieza or drew from him in any way. It kinda tired Goku, and all his friends verbally decided to contribute their energy to the SB. After, Piccolo was impressed Krillin and Gohan could fight "after giving so much energy to the SB."
Apparently, at some point in the Buu saga Goku wants to create a SB, and he gets Hercule (Mr. Satan) to tell a crowd of people to lift their arms - thereby contributing to the SB. This is what makes me think that intelligent beings have to will their energy to a SB - it can't be stolen from them. Again, w/ planets, animals, rivers, etc. it could be they have no choice but to aid a SB, or it could be a wierd form of instinct that lets them will it to Goku, who they all like (cuz he's so pure-hearted, yadda yadda).
- Just my observations from the show, nothing official's ever indicated that.