Ian and David, it takes experience to learn how to handle a boat in current. A lot of it is simply an educated guess of how far the current will carry you and adjusting for it in the process. For example, when you are picking a rider up you may need to either over or under shoot the rider and let the current do some of the work. In fact that's one of the mistakes I see a lot of people make...trying to "beat the current". Dont fight against it, just accept it and compensate, using it to your advantage.
David, we "drive onto" our trailer in current. For my personal boat I put the highest point of the trailer fenders about even with the water line. This allows me to come in a little quicker and let the trailer slow me down. You still need to come in straight otherwise it can get REALLY bad, but if you can drive it straight on...you can keep the trailer a little higher out of the water and come in a little quicker. This will help offset some of a side current's impact.