When is a web page spam?

Interesting conversation over in Danny Sullivan's SearchEngineWatch forums about what constitutes spam in search engines. First, the usual heated, lengthily debated arguments about techniques and degrees:

1. using certain techniques, or using any techniques at too high a degree is spam;
2. optimizing pages at all for search engines is spam;
3. there is no such thing as spam;
4. what search engines think is spam is spam;
5. what users think is spam is spam;
6. what some SEOs think is spam is spam.

Then, a turn: since SEOs as a group can never agree on what is spam, much less degrees and techniques, why not a discussion of the risk factors of optimization techniques?

I'd say: risk factors against effectiveness.