I don't know of a hard and fast rule, but here's a thought. All of those 'strikers, suers, compelers, haters, abusers, and persecutors' are doing that to YOU...unless you are the one doing it to THEM. Could even be 'mutual', I reckon...but Jesus is talking to US. I don't see in there "seek those people out".
What is impossible for man is possible for God.
Here's how Paul said it:
Rom 12:14 Bless those that persecute you; bless and do not curse.
Rom 12:15 Rejoice with those that rejoice, and weep with those that weep.
Rom 12:16 Be of the same mind toward one another. Not minding the high things, but associating with the humble. Do not become wise in your own opinion.
Rom 12:17 Repay no one evil for evil; providing that which is good before all men.
Rom 12:18 If possible, as much as depends on you, keeping peace with all men.
The way I see it, these people are actually in your life...close enough to 'strike you on your cheek', after all. They are not nebulous people floating around in the culture. Why would you be concerned with those at all? Think on whatsoever things are pure, and lovely, and true and of a good report. Save your 'returning good for evil' for those God puts you in direct contact with. MAYBE that includes people on the internet too.
Here's a great study Ray did on "love" and its quite practical application.
http://forums.bible-truths.com/index.php/topic,3719.0.html