There is a +1 to the DC for perception when trying to see something for every 10 feet away it is from you. Therefore, you have a chance to see things that are less than 200 + 10*perception modifier feet away; if things are more than 100+10*perception feet away, you can't see them by taking 10, so that's about when I'd be rolling to see things. Of course, that assumes the object to be seen is average sized and there's neither favorable or unfavorable conditions. Darkness, objects in between, and so on will reduce visibility.
Of course, this is a bit silly: If a visible medium-sized creature (base DC 0, as per the "notice a visible creature" line; this creature is not attempting to use Stealth) stood at one goal-line of a football field and you stand at the other goal-line (300 feet away), you could only see him on a roll of 20 with a +10 to perception. Take ten and you have no idea he's there.
(It might not be as silly as it seems: Atomic Think Tank, the Mutants and Masterminds message board, found that, based on the known data for 20/20 vision in terms of spotting a human being not trying to hide, and distinguish some small number of details, the maximum distance is approximately 1 km. This neatly works out to the distance penalty for vision being +1/100 feet if you assume Taking 10 and a +0 to your Notice check.)
For ultimate silliness, @DuckTapeal points out that "the penalty to see the sun at noon is roughly -42 million". Of course, the size penalty for spotting a creature 30' by 30' is +8, and it goes up for each size category above that, so... What size category is the sun?
As @KRyan points out, by RAW, “The sun is colossal, because there is no size category larger than that. Colossal covers everything that is ‘64 ft. or more.’ That said, each size category is twice the size of the previous category, so we can extrapolate larger categories; if we do, the sun is about 232 ft. in diameter, or 26 size categories above colossal. However, the size penalty is just −4 per size category, so it would be −116 for 26 size categories above colossal.”
In short: The party can see as far as you want them to be able to see, unless the range is under about 50ft or so, at which point the rules make sense again.