Although they say that it ONLY uses idle cycles, the Seti client isn't at the lowest priority. Unlike most DC clients which are at priority 1 (the lowest possible), Seti is at (i believe) priority 4 (all out of a scale of 20 if i remember correctly). That is why Seti seems to take priority over other DC projects, and also cause some of the problems with some other programs.
Not the best situation, but Seti and UD were an OK combo, because with UD you got more points the longer it took IIRC.
Other thing is to run one project on one computer, one project on another computer.
Post your rigs here and we'll be able to tell you what rig is best for what project, and you can make your mind up based on what is best 🙂
ConfusedBW