In the field of divorce litigation, social networking is not just helpful in uncovering a cheating spouse -- which, in our Canadian, no fault divorce scheme doesn't really matter anyway -- but in uncovering other information that could assist a party's case.
In the case of a cheating spouse, information learned on Facebook and other social networking sites can certainly be a catalyst for the end of a marriage or other relationship.
Information on a spouse's behaviour, reckless or otherwise, can be of assistance in custody proceedings.
Much can be gleamed about a party's parenting or lack thereof by way of status updates and photos posted on Facebook.
In the case where spousal support is at issue, a spouse can learn information about the payor spouse's financial situation. Did he just buy a new vehicle? Was she looking at a cottage property? And a payor spouse can learn about a recipient's situation. Did he/she just update their relationship status? Maybe there is a claim that another, third party is responsible for support and maintenance of a former spouse.
More often, we see parties using social media as a tool to uncover information related to their former spouse that can assist their own case. Sometimes this information is helpful to a material issue in their matter, and sometimes it simply goes to credibility.
In my own practice, I have cautioned clients about what they post because it can come back to haunt them not only in the course of their divorce/separation proceedings, but it may also undermine the already-fragile relationship they have with their former spouse, and potentially with their children. (Children don't want to learn all about mom's new boyfriend on Facebook, and dad doesn't need to learn that his wife just went away for the weekend with her new squeeze).
In cases where there is an assessment underway, what a party posts on their social networking page could also impact on the results of that assessment. Increasingly, parties are doing their own investigation work by way of social networking outlets. This sometimes means that parties are using someone else's social networking credentials to gain information about their spouse -- often, this means "breaking into" a child's Facebook account.
This can also be problematic in that privacy is being compromised; the child's right to privacy, although limited, and a spouse's right to privacy given the information they are posting is not meant to be viewed by their former spouse who is certainly not a Facebook "friend."
Other non-legal issues flow from this including a breach of a child's trust and the deterioration of that relationship in pursuit of an upper hand in the divorce/separation proceedings.
In short, social networking can go way beyond assisting parties to uncover whether or not they have a cheating spouse, and then again, you don't need to use Facebook to determine if your spouse is a cheater -- Apple already has an "app" for that.