Karen and I saw The Lake House on Sunday, and I highly recommend it. Don't expect to have the time-space-continuum explained, though. It leaves it to your imagination, and maybe that's for the better. This film is not about the science. It's for the poet and lover. As Karen said, "It's just magic." I could hardly argue.
Apparently, John Cusack was asked to play the lead, but he declined. Keanu picked up the part very nicely, and I don't know if I could see anyone else in that roll pull it off as well as he did.
It's interesting to note that another Chicago time-travel film is in the works.