From what I saw on personal experience with my sites and site of my clients on reciprocal link building - under 100 links per week is more than safe.
What is better.
Links must be relevant.
Links should better be on nice PR pages.
Links should be on trusted resources.
The last issue is the most important and gossiped. After reading Colin McDougall's VEO report I saw that he also claims for Google to rely a lot on the trusted resources. So, even if you get tons of links within a short period of time from TRUSTED resources - no problems at all, even if these resources are irrelevant to your niche (yes, I told this scary word, it was not an illusion).
The biggest problem is what exactly sources are relevant. Because Google is not likely to share that info. Only hints. For example, Yahoo is *reported* to be included to trusted sources, USAToday, majors in different spheres of life.
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