'They love it' or 'They are loving it'?
When a verb describes a state and not an action we do not use the continuous tense. For example, 'play' is an action so we can say 'playing' whereas 'be' is a fixed state which does not change: 'To be, or not to be'.
Grammatically it is not correct to say "Im loving it" even though McDonald's have made this expression famous. 'Love' is a state verb and so we should say "I love it".
State verbs generally fall into 4 groups:
Emotion: love, hate, want, need
Possession: have, own, want, belong
Sense: see, hear, smell, seem
Thought: know, believe, remember
Here are some more examples of state verbs:
Some words can be state verbs and action verbs. The meaning of these verbs is then different. Take a look at these:
'I have a car.' – state verb showing possession
'I am having a bath.' – action verb which, in this case, means 'taking'.
'I think you are cool.' – state verb meaning 'in my opinion'.
'I am thinking about buying a motorbike.' – action verb meaning 'considering'.
Link: More help with State Verbs