I saw someone asking about "fleet arcing" in another thread, but I can't find that post now.
Here is a nifty trick to get your ships in a "pseudo arc".
Build a bunch of rally posts on one of your planets in a somewhat arc like fashion. Send your fleet into the planet (sending them back out first if needed), and your ships will somewhat "spread" over those rally posts on that planet. This is because when there are multiple rally posts on a planet, each incoming ship chooses one at random. Thus if you have them in a nice shape, your ships will, on average, spread out over those points.
At this point, formation move (bound to J+<order> by default, IIRC, like J+right click move) might come in useful, as that will cause your ships to keep their relative positions as much as possible (obviously, breaking it at points where they can't anymore, like going into wormholes, but they should then try to get back into position when they can). The "sticky formation move" control might help with this (it makes formation move be "remembered" a bit longer and under more circumstances), as well as combining it with group move (so different movement speeds don't break the formation while in transit).
This also works for pretty much any rough shape you try to make out of rally posts.
Obviously, the arc case worked better when circular place was in the game (come to think of it, we got line place back, when are we getting circular place back?), but you can still do a decent job by hand.
EDIT: An old trick I discovered way back in the version 3.XXX days, but only now thought to post it. Hope some of you can do some nifty stuff with it.
EDIT2: Yes, you could do this manually by placing chunks of your fleet yourself, but given how large fleet sizes can get in this game, this can quickly become way to tedious. This is a nice way to do it, sort of, automatically, and it even lets you "save" that shape to quickly reform it for later, instead of having to do it by hand each time.
