It's interesting how answers change regionally. Dutch and Dave and I have a viewpoint several hundreds of miles apart.  Here is SE Illinois we would give a few answers differently.

1. Same as Dutch except I don't know anyone who has ever tried planting in a circle.

2. There is some done, but not a lot.  Most of us don't want the added attention from the EPA if something messes up.

3. Every system has an end gun on it. It will also have a booster pump to operate the end gun if it is electric.  In theory it gains me 22 acres on a quarter section system.  In practice it doesn't because a half mile field is shorter than 2830 feet.  But it is Standard Operating Practice here.

4. Swing arms (we call them tails) are common ... most do not have them but they are fairly common  They are reasonably cost effective and a maintenance problem, The cost effectiveness is directly related to crop value.  The more you make off a crop the more an irrigated corner is worth.  It also gives the repair guys some job security.

Oh, and looking at your next question, tails always have end guns.

5. I do not think an end gun is as accurate as the main system, but yes, any water is better than no water.

Our irrigated fields are typically round with flat sides.  We are getting more and more "windshield wiper" systems as all the "easy" irrigating has been done and now we are trying to fit systems into less than perfect areas.  I will attach a couple photos from 2006 showing typical systems in our area.

The first shows a couple dry corners.  It is also show in the next photo.  Ours has a tool shed on it.  That corner is in milo, which is why it is so dark.  Both field are in seed corn, which is why the ends look so ragged.  There are no end rows. The field in the lower left is watered with a "recycled" water drive system and planted in soybeans.  What doesn't show is shortly after this was taken he pulled a traveling gun straight west beside the 3 little bins and watered his dry corner.

The second photo gives more perspective. None of the systems shown have tails, just end guns.  If they did not have end guns the watered area would be round instead of square sided.

If you look in the lower left corner you can see a traveling gun in operation.  He has two long narrow field he waters with one pull.

The full circle is 2-80's that own the system in partnership.

The 2 systems in the upper left are setting just off the property line and one farmer is buying water off the other farmer.  The middle system shown also feeds a 300 ft system on the right side of the photo that is towed back and forth to water a 1/2 mile long 40 acres.  It also catches the dry corners on the 80 the main system is on so there are almost no dry corners. There is a 1/4 mile pipeline from the pump to the field, then 300 ft pipeline each way to the pivot points.  The pump is set up for 800 gallons a minute on a 1300 ft system, so to get it to feed a 300 ft system the small system had to be nozzled to handle the volume.  If you stand under the end of it you REALLY get wet quickly.

edit: Didn't know I could get so many typos in one paragraph

(NAT Photo 01.JPG)

(Ledermann and Drake Place from NE (Small).JPG)

NAT Photo 01.JPG (37KB - 322 downloads)

Ledermann and Drake Place from NE (Small).JPG (24KB - 318 downloads)