According to the Tofugu particles cheat sheets, Koichi says the following about で:

Show Context
Meaning: “By way of” / “At”
Can show how and where an action takes
place.

Examples:

くるま　で　いきます。
I will go by car.

わたし　は　レストラン　で　たべた。
I ate at the restaurant.

The free Nihonshock cheat sheet says the following about で:

Marks a place, area, or length of time inside which something occurs.
Marks a method, tool or circumstance under which something happens.
Marks a material or substance; composition.

The grammar dictionary says で indicates the time something terminates, or the amount of time a period of activity has taken place. By comparison, に indicates a point in time at which something takes place.

It clarifies the difference between に and で by giving an example where either particle is grammatical:

春学期は五月十日(に/で)終わる (The spring term ends on May 10th)

When で is used, the nuance is that the spring term lasts up to May 10. When に is used, however, the sentence simply indicates the time when the spring term ends.

And also a few sentences where only で will do, like 木村さんは三日でこのレポートを書いた (Kimura-san wrote this report in three days).

I’m thinking the difference is something like that between に and へ. =)

They’re kinda like the difference between “to” and “toward”, though they’re fairly interchangeable.