I am right at the limit for my rear brake lines---I plan to get longer rear shocks when I get a new springpack made, and when I do I will have to get longer brakelines. There is probably about 1/2" total slack left in the lines when my Rancho 9116's are at full extension. The diff breather also only has an inch or so of slack left.
The front ones seem okay, if I had another 2" of downtravel than I do I'd have to worry about them (then again, if I had another 2" of downtravel, I'd be so happy I wouldn't be worrying...
).
I think you've seen the pics on my website...when I wheel, I wheel hard.