FWIW, I currently have 4 1-wire devices hooked up to my Arduino,
2 1820's and 2 18B20's and have not had a single problem although
the distance between the Arduino and my sensors is about 6-inches (15-cm).
[Yeah, I know, not very useful 'cept for testing the sensors]
Longer runs will probably require a stronger pullup resistor (lower
resistance) on the data line (I'm using the standard 4K7-ohm resistor)
and probably low-capacitive cabling like CAT-5 or 5e. Longer runs
may possibly preclude the use of parasitic power and require Vcc to
be brought down the cable as well.
Dallas Semi (now part of Maxim IC) has a number of documents with
regards to longer 1-wire network cabling if that's what you're dealing
with.