There are situations where it is very useful to know roughly how much time it will take to travel in warp between two points. If you have a bait ship somewhere, it is good to know how long it'll have to survive until the main fleet arrives. Or if you're in smaller ships and want to use the difference in warp speed to split an enemy gang, knowing the exact time it takes for any ship to warp a specific distance is very useful.
The maximum warp speed is easy, but in most situations the acceleration and decelaration in warp as well as the align time are the more important factors. What I'd like to know is a rough formula that would enable me to quickly estimate the time it'll take a specific ship to warp a specific distance.