Earlier this morning their was a thread about how half time adjustments seem to be have greater effect this year than most years. I think it may well be because of the sideline computers. Not only the players but the coaches see things they didn't until told by the people in the booths. From the field level you can't begin to see the whole field. The computers allow the coaches at field level to get a better view of the field. They then begin to mentally make adjustments and use halftime to verify with the booth coaches and implement them.
Defensive changes seem to be the most effective (or at least more noticeable). I think offensively you have to continue to do what you do, but adapt to what the defense was doing in the first half. If you are a running team you probably can't suddenly become a big play passing team after half time.
I may be wrong but I think next year we will see even more teams defensive adjustments in the 2nd half as coaches see the usefulness of the tool.