Thank you everyone for the input. You've given me a lot to consider.
Just to clarify - I want to buy the longer lenses because I shoot primarily birds and nature.
I like the Minolta but I don't really have anything to compare it to as the only other cameras I've owned have been point and shoots.
It all boils down to whether it's worth the expense to buy the 400mm and 600mm lens for the Minolta if in a year or even 6 months I find out that there's a significant difference in quality from Minolta to other brands. My photography budget is really tight so I want to weigh out the advantages and disadvantages now. As I said before, Minolta users seem to be few and far between. It just occured to me that there might be something about the Minolta's that I wasn't aware of.