On the upside, there's a tremendous amount of available energy for lifeforms to harvest.

Here on Earth, life gets its energy from soaking up solar energy, or from eating things that have been soaking up solar energy, or from eating things which have eaten things which.... you get the idea. The sole exception is at deep-sea geothermal vents, where you can pick up energy from the thermal gradient. On Gliese 581g, there's huge amounts of energy to be picked up just from the constant flow of energy from hot side to cold side, so I'd expect lifeforms to somehow be tapping into that.