Whether you find the conclusion of the film as a triumph of love or a cynical assertion that these two characters are doomed to a self-perpetual cycle of co-dependence (something hinted at in an excised denouement in Charlie Kaufman's script that didn't make the final film), or hell, both, is really besides the point, the essential message I take is something much simpler: keep the bad memories, because they are just as essential a component of our lives as the happy ones.
I saw Eternal Sunshine at a particularly poignant moment in my life: a few months after a long, and similarly doomed cyclical relationship had finally come to it's end. While painful at the time, the film helped me in some small way to appreciate the moments I had with that person and I met my wife within 10 months of catching it opening day (celebrity sighting/gossip: I had a conversation with Sarah Silverman and her sister who were companions of one of the friends I saw the film with on the merits of Michel Gondry's work after the showing, and it was refreshing to see the usually sardonic comedienne notably touched by it's artistry).
Here is the film's equally brilliant trailer which opens as a commercial for the Lucana corporation before morphing into a dialogue light quick montage of moments from the film set to ELO's "Mr. Blue Sky". From the first time I saw the trailer theatrically in the fall of 2003, I knew the film would be special, although I could not foresee the particular connection that I would, and still, have to it.