R2D2 didn't activate the hyperdrive, Vader did

Rating: 10/10 (11 December 2006)

Although R2D2 was told that the hyperdrive was deactivated, it was made clear by C3PO that R2D2 had "illusions of grandeur" in thinking it could reactivate the hyperdrive on the Millennium Falcon. Also, notice that Vader was trying to reach out to Luke (on the Millennium Falcon) showing signs of a "father/son" bond. The clincher is when Vader is looking at the Falcon and the hyperdrive is suddenly activated. Shortly after, the Admiral, who was to have deactivated the hyperdrive, is taking one big gulp awaiting Vader to punish him for this screw-up. However, Vader solemnly walks out of the room with no show of anger.
As such, I think it was Vader, and not R2D2, that re-activated the hyperdrive. This was the first sign that Vader was weathering an internal struggle between the dark side of the force (Emperor) and Anikin's love for Luke. A struggle that Vader looses in Return of the Jedi.