I just wrote three big comments on @JeromyAnglim's answer, but I'm opting to move them all to this answer instead. This isn't an attempt to answer the OP completely, but hopefully they'll be of some use for part of the question.

From a mainly statistical and psychometric standpoint, I've heard (from an expert whose opinion I could mention confidently in a manuscript I'd intend to publish) that adding point options to extend a Likert scale tends to increase the size of the general factor (in principal components / factor analysis). This could be due in part to bias of the sort Jeromy mentions. Thought that might be useful to add.

Another consideration is how one anchors those extra points. Being ordinal, a Likert scale can deliberately deviate from symmetry and even spacing between options in potentially useful ways. E.g., ratings from -1 to 5, or adding more extreme ratings like, "0 - Absolutely not at all whatsoever," or "6/max - As much as I could ever imagine for anyone ever in the history of humanity and within the laws of physics as we know them." These are slightly absurd wordings that I wouldn't recommend verbatim; slightly terser and more meaningful wordings might be more useful. In general, extreme wordings may serve to reduce ceiling/floor effects somewhat. On that topic, see also: http://cogsci.stackexchange.com/q/4776/4086.

However, including anchors that are worded even as absurdly extreme as those I mentioned above might actually help for discriminating between useful, meaningful responses, and inattentive or biased responding, as where a person pays more attention to the number than the meaning you intend to assign to it with the anchor. This is one way of addressing the methodological problem of interpreting Likert scale responses and identifying response bias in general (though it's an untested idea of my own invention as far as I know).

I just wrote three big comments on @JeromyAnglim's answer, but I'm opting to move them all to this answer instead. This isn't an attempt to answer the OP completely, but hopefully they'll be of some use for part of the question.

From a mainly statistical and psychometric standpoint, I've heard (from an expert whose opinion I could mention confidently in a manuscript I'd intend to publish) that adding point options to extend a Likert scale tends to increase the size of the general factor (in principal components / factor analysis). This could be due in part to bias of the sort Jeromy mentions. Thought that might be useful to add.

Another consideration is how one anchors those extra points. Being ordinal, a Likert scale can deliberately deviate from symmetry and even spacing between options in potentially useful ways. E.g., ratings from -1 to 5, or adding more extreme ratings like, "0 - Absolutely not at all whatsoever," or "6/max - As much as I could ever imagine for anyone ever in the history of humanity and within the laws of physics as we know them." These are slightly absurd wordings that I wouldn't recommend verbatim; slightly terser and more meaningful wordings might be more useful. In general, extreme wordings may serve to reduce ceiling/floor effects somewhat. On that topic, see also: https://cogsci.stackexchange.com/q/4776/4086.

However, including anchors that are worded even as absurdly extreme as those I mentioned above might actually help for discriminating between useful, meaningful responses, and inattentive or biased responding, as where a person pays more attention to the number than the meaning you intend to assign to it with the anchor. This is one way of addressing the methodological problem of interpreting Likert scale responses and identifying response bias in general (though it's an untested idea of my own invention as far as I know).