So here's what I think:
At this point we need instant replay in baseball because quite honestly viewers at home could be doing a better job than the actual umps.
-Have a fifth umpire that sits up in the booth
-When a review comes in, no need to stop play and huddle around a TV then talk about it, just have the fifth ump make the call and move on, I think the entire process wouldn't need to take more than 15 seconds
-Reviewable plays: Home runs, tags on all bases, catches in the outfield, and tagging up (though I don't think it would come up often)
-I don't think balls and strikes should be reviewable.