I would consider this Google Groups thread a "gem thread," since you don't always see a thread at this level - it is precious. A Googler, Wysz, discussed in detail four methods of hiding content and how Google may interpret each method.
Hidden Links via Positioning/Color, for Design/Accessibility: Wysz explains that this method can bring you "dangerously close to a grey area." The example he gives is that if you use the word "SkipToContent," which "isn't likely to be interpreted by anyone as an attempt at deception", said Wysz. He then adds, and this is important, "unless the term "SkipToContent" becomes a highly competitive keyword." Wysz does go on record saying, "If implemented in a non-deceptive manner, these aids should not cause a problem." But that leaves it up to Google to decide and intent is not always easy to judge. So, try not to use this method, if possible.
Hidden Links with No Mention of Accessibility or User Value: I think I will just quote Wysz here, cause he said it best. :)
I'm going to assume that these links are only intended for bots to see as attempt to deceive search engines. That's probably not an assumption you want a Googler to make. When making this judgement on your own, just ask yourself this question: "Is all of this text here for the user?" If you want to make Google (and your users) happy, the answer should always be "Yes."
Forum discussion at Google Groups.