I have been doing some research on horizontal pit loops and had a few questions and would appreciate it if anybody can help out. 

1.   What is the proper way to go  from row to row, do you make a big curve at the end, or cut pipe and fuse an end fitting?
2.   With Waterfurnace systems there is a 1' gap between pipes, is there a max as to how wide you can go?
3.   Has anybody seen issues with performance of these systems?

Pit loops work fine. You just have to move a lot of dirt. Making a curve at the end is the best way to go as long as you don't kink the pipe. Going wider does not gain you much, and you have to move more dirt.

Not sure of your area, location in the country. Hopefully there will be some moisture in the pit. Moisture and improper backfill/compaction is the main things to be concerned about that I know of. Others please verify. We don't do pit systems, only vertical exchangers.

All about footprint, you pick. As long as you have a big enough heat exchanger; shape doesn't matter. Dan also makes a great point about compaction. Make sure your backfill strategy addresses a good contact between pipe and soil (see Linda Piazza's toils). DX systems bury soaker hoses with the loops that are employed for 24 hours after backfill to ensure good interface (I suppose as an added bonus the tinkerer could even turn it on when it was super hot out for a boost to performance).
Good Luck,
Joe