My thought is, the two are dramatically different from each other, yet they can (and often should) co-exist in a solid relationship between spouses (or partners).
When we were young, lust is about all we knew. When that hot classmate walked by, I don't think too many of us thought about how we could build a life with that person. In most cases, we just thought about how HOT they were (if it was a concious thought at all).
Lust is an urge, a desire, a need to consume. It is VERY similar to avarice, and certainly isn't limited to sex. Lust should never be confused with love, since lust has a "hook" every single time... "If you love me, you'll have sex with me" is a good example of that.
Like lisagirl said so eloquently, it is at its core SELFISH. It's self-centered.
Love, on the other hand is an enigma that is far more than an emotion. It's more than a commitment. At its very core, it is self-less. Love (especially in the divine) is pouring your life into another.
Love has no hook, there are no expectations, and is as much a choice as it is an emotion. I love what Scripture says about love:
QuoteLove is patient, love is kind. It does not envy, it does not boast, it is not proud. It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres.
Love never fails. (1 Cor 13:4-8a, NIV)
This passage speaks of the true nature of love almost completely.
The problem in some relationships is that there are times when the one who lusts is literally draining out the life force of the one who loves. The "lover" is pouring their life and heart into the "luster," who's doing nothing more than consuming. In the end, both are left empty.
I think it's important that we all reflect in our own lives whether we're truly giving as much as we're taking. Sometimes, our relationships depend on it.