As an American, I can confirm 'I'm loving it' is a common phrase, and also grammatically incorrect.
'love' is an action verb. In the above sentence it is being in a stative sense. McDonald's popularized the expression, using it as their slogan.
Some verbs can function as both action verbs and stative verbs.
Here are some examples:
BE
<ul><li>
Stative:</li><li><em>He </em>
<em>is </em><em>immature. (he is always immature)</em></li><li>
Action:</li><li><em>He is </em>
<em>being </em><em>immature. (he is temporarily acting immature)</em></li></ul>
HAVE
<ul><li>
Stative: possession</li><li><em>I </em>
<em>have </em><em>a car. He </em>
<em>has </em><em>a dog.</em></li><li>
Action: expressions with “have”</li><li><em>I’m </em>
<em>having </em><em>breakfast (eating breakfast).</em></li><li><em>He’s </em>
<em>having </em><em>fun (experiencing fun).</em></li></ul>
SEE
<ul><li>
Stative: perception with your eyes; understanding</li><li><em>I </em>
<em>see </em><em>some birds.</em></li><li><em>I </em>
<em>see </em><em>what you mean.</em></li><li>
Action: meet; have a relationship with</li><li><em>I’ll be </em>
<em>seeing </em><em>the doctor tomorrow.</em></li><li><em>They’ve been </em>
<em>seeing </em><em>each other for a month.</em></li></ul>
LOOK
<ul><li>
Stative: appearance</li><li><em>That cake </em>
<em>looks </em><em>delicious!</em></li><li>
Action: directing your eyes to something; phrasal verbs</li><li><em>He’s </em>
<em>looking </em><em>at the computer screen.</em></li><li><em>She’s </em>
<em>looking for </em><em>(= seeking) a job. </em></li><li><em>They’re </em>
<em>looking after </em><em>(= taking care of) my dog for the weekend.</em></li></ul>
SMELL / TASTE
<ul><li>
Stative: the quality of smell or taste possessed by something</li><li><em>The bar </em>
<em>smells</em><em> of smoke.</em></li><li><em>This meat </em>
<em>tastes </em><em>like chicken.</em></li><li>
Action: when a person uses their nose or mouth to test something</li><li><em>He’s </em>
<em>smelling </em><em>the cookies.</em></li><li><em>She’s </em>
<em>tasting </em><em>the soup to see if it needs more salt.</em></li></ul>
THINK / FEEL
<ul><li>
Stative: when talking about your opinion</li><li><em>I </em>
<em>think </em><em>that’s a great idea!</em></li><li><em>I </em>
<em>feel </em><em>that this is not the best use of our time.</em></li><li>
Action: when using your mind, or experiencing emotions or health issues</li><li><em>We’re </em>
<em>thinking </em><em>about moving to another city.</em></li><li><em>I’ve been </em>
<em>feeling </em><em>unusually tired lately</em>.</li></ul>
WEIGH / MEASURE
<ul><li>
Stative: when talking about the quality possessed by something</li><li><em>The suitcase </em>
<em>weighs </em><em>20 pounds.</em></li><li><em>The surfboard </em>
<em>measures </em><em>2 meters by 55 centimeters.</em></li><li>
Action: when a person performs the action of weighing/measuring something</li><li><em>The butcher is </em>
<em>weighing </em><em>the meat on the scale.</em></li><li><em>The architects were </em>
<em>measuring </em><em>the distance between the pillars.</em></li></ul>