Clay killing Piney could be seen from a mile away, but man was it sad. After all Piney's done for the club--described numerous times during the episode--Clay ends his life just like that. We know Clay is a bastard, but it's been a long time since a character was killed (the last, I believe, was Half Sack back in the second season), which amplifies the impact of the killing. Then again, one could argue that Piney doesn't do anything and wouldn't be a big loss, and that Clay killing him wasn't shocking based on a pattern of behavior.
"Family Recipe" dangles a bunch of disparate threads with no resolutions, and we get a good sense where the last part of the season is headed. Tara is headed out of town, Charming may be wrested from Hale with help from Roosevelt's wife, and Chibs now knows about Juice's suicide attempts.
Most important, the cartel violence is a daily part of their lives. Everyone is scared of what may happen, and I can't blame them considering the level of brutality. It does seem a little convenient, however, that no one in SAMCRO has been touched yet. And, given that Piney just died, it's unlikely any of the principles will be killed. Clay pinning Piney's murder on Lobos Sonora seems like a big catalyst, but the characters should be able to sniff out that the murder was not in the same style as the other murders.