I'm not a fan of ribbons. They're very, very smooth...Too smooth for my taste. There's no 'oomph' at all. They make nice mics for narration and they have a musical quality for sung vocals. They can also handle extremely high SPL levels, which makes them good for bass and guitar cabs. If you want a lifeless, plain (but clean and detailed) sound, ribbons can be a good choice.
On the downside, most typical pres won't do them justice because they require a huge amount of gain. You really need a ribbon pre. They're also not rugged at all. A drop, phantom power or a plosive blast will ruin the mic.
Emmett