From an UGC perspective, if Google is writing off all the links from forums and the likes, it is contra to what they proposed recently "People share a lot these days". All these sharing is done by users and how long do you think the sharing phenomenon can be genuine?
Yes, people abuse forums, signature links etc. but anything can be abused these days and we have seen it recently in the form of two big examples.The only difference is the former (forum and sig links) is low profile while the latter is high profile abuse.
A generic demotion of this sort will definitely impact a number of genuine ones too. There are a number of genuine shares in those forums and it wouldn't be good to negate them.
I do think that instead of devaluing/changing something, it will be better if google is innovative enough to find new positive signals to promote the good pages higher.The system is anyway going to be gamed but these new signals will ensure that the cream will pop up.Reworking on existing factors is a big fail for me.
Hey google, do you have a job.I would love to be part of it :)