It may depends on the conduit and cable size but: How far can you go and/or how many 90's before a hand hole/pull box is required for pulling wire? (3)350kcmil for an underground service lateral from a pole to a meter on the side of a building.
As a general rule, I agree with iwire, common sense. Now I thought that I had read that you can run a max of 600' underground between manhole/handhole, but I am starting to think that is a local PoCo regulation, bacuase I can't find it again in the NEC...
The only other limitation I can think besides conductor damage is the pulling method. If you have a 240' fishtape in a 250' run...
I try not to rely on breaking the run at a coupling to pull in a rope of string, it's just not fun! Easier (I think) to set a box as you run the conduit.
The utility (actually their contractor) is the worst about "pullable" laterals around here. I watched them put one together 20' at a time as they pulled the wire in and there is no way it is ever coming out. They dropped the wire in the trench and threaded the pipe over it, gluing as they went, sand and all.
I was not there in any official capacity so I could just shake my head.
We put in a primary once that was (don't yell at me, we followed Dominion VA drawings) 540' of 6" PVC with 5-90's and 1-45. Some of these guys live by rules than make me want to cry! We tied a pull-string to a 20' piece of dead fishtape and pushed through the conduit as we ran it. Made sure to pull the string line back and forth as we lay conduit. If it gets stuck in a glue joint, GOODBYE!
To top it off, we trenched 48" to lay the primary and three weeks later the site guys dropped 36" of fill on top (before the PoCo pulled the feeders)! They got their lines in no problem, and we all wept for joy.