Tried adding a feed from multiple users but the plugin returned an empty result. Used syntax [twitter_stream search='from:user1 OR from:user2 OR from:user3']. Same search pattern on http://twitter.com/#!/search-home yielded the proper result, so it seems to be a plugin bug. Same search but with "@" instead of "from:" yielded the expected results, so there's something about exactly "from:" that the plugin doesn't handle right.
Tested that with a single 'from:user1' search attribute and the plugin returned nothing.
As an aside, in the documentation the plugin uses " as an attribute delimiter, except on WP.org plugin front page, where ' is used instead. Both work. I suggest using (and possibly allowing) only the latter, because " is a Twitter search operator. You can for example search for "beer pong" to exclude search results that say "ping pong and beer". But a user who has read through the documentation and seen " be used by the plugin, is stuck with trying to figure out whether [twitter_stream search="#beerpong OR "beer pong""] can possibly be made to work.