Getting a custom view of Twitter and Facebook posts
I have clients who require exactly the same feature, and the best method I have found so far is using Feeds and Feeds XPath Parser. 

I create two Feeds importers that import from the RSS feeds of the client's Twitter and Facebook profiles. I set Feeds to create a node for each update (content type 'Social update') and use Feeds XPath Parser to populate the correct fields (title, body, timestamp, etc). I also set Feeds to automatically purge imported nodes after two weeks, and set it to schedule import on cron every hour.

Now I have each new post in a node, and I can display them however I like using Views.

This works ok, BUT I'm not convinced it's an optimal solution. I've looked at modules that interface with the Twitter and Facebook APIs for a better solution (e.g. Twitter Pull, Facebook Pull, Feeds Facebook Parser, Twitter) but they don't seem to provide a method for pulling Tweets and Facebook posts together in a single view or block. I'd love to get some more ideas on this.