I noticed one of the 4 example pictures of 30' lines that doesn't seem to work. Look at:
http://paizo.com/pathfinderRPG/prd/magic.html
The second (from the left) example 30' line is actually 35' long. It is obvious that the only way for the line to travel the path indicated is for it to be started at the casters upper corner/intersection square, which means by the time the line shifts over one square like it does it has traveled a second diagnal, but this doesn't seem to be accounted for in the diagram. Assuming the spell also has a 30' range the final square is within 30' of the caster, but the line itself can still only travel it a total of 30'. So had the caster started the line at his upper right insection/corner instead it could hit this ending square, but the resulting line would look like the first example line, only shifted one square to the right.
The opposite of this is another rules problem I have. If you apply the widen spell metamagic feat to a lightning bolt you increase the spell's listed area to a 240' line, but since the spell's range is unaffected and remains at only 120' the line can not effect anything further away than 120'. This is specifically stated under the Range heading on the same link.
If any portion of the spell's area would extend beyond this range, that area is wasted.
Also note that most cone spells can not be increased in size because they are limited by range rather than area, and they do not qualify for enlarge spell because their ranges are fixed rather than being short, medium, or long.