I have no comment on the 'love the sinner', but about hating the sin. Surely, in Islam we should hate the sin.
The Prophet (peace and blessings of Allaah be upon him) said: “Whoever among you sees an evil action, let him change it with his hand (by taking action); if he cannot, then with his tongue (by speaking out); and if he cannot, then with his heart (by hating it and feeling that it is wrong).” (Narrated by Muslim, 49).
My personal opinion to the 'hate the sinner' is that we shouldn't do so, coz' we can't really know if the person has repented from the sin or not (or if he feels bad doing it) or the reasons for it. My point is that we can't judge him by that sin he commits without having the sufficient knowledge. On the other hand, I think it's ok to judge a person based on his deeds such as Hitler or Osama. But that person might do alot more good deeds that we don't know of. Allah knows best.
Edit: To add an example- My uncle was killed by a ruler. Overall the ruler was a good person. He gave people their rights and granted them justice and security. Regardless, many ignorant outsiders use the killings the ruler committed (my uncle among them) as a justification for their own parties' wrongdoings, though, in fact, he did it for a just reason. Now I could've hold a grudge against him for that action he committed if I would've been judgmental or inconsiderate.