From the upcoming 2.001B release notes:
-The descriptions of dreadnoughts have been updated to reflect the fact that they are no longer good against force fields. Additionally, dreadnoughts have gotten a boost in general, with new bonuses against munitions boosters, zenith bombardment ships, teleport battle stations, fighters of all sorts, zenith autobombs, raiders, and tele-raiders. This makes dreadnoughts a much more versatile and interesting ship in general, especially against the power of massed AI zenith bombardment ships.
Also, ships in general that damage engines should switch targets when the engines are out on a target if there is a better other target nearby, and if you didn't explicitly give them an attack order (ships that are explicitly ordered to attack a specific unit will never switch targets until given a new order). That should be the case in 2.0.