I like this person's interpretation (from Pain-in-the-English-dot-com:
Originally Posted by Clark
LowB | Feb-2-06 3:44AM__________________________
As is usualy the case, grammar might just not keep up with the actual language spoken by people today. On the other hand: one of the basic usages for present continuous is 'an ongoing action around now'. If I'm eating at that food company at a certain time, I'm loving it at that time. That feeling goes away after a while though, that's for sure.
I'm lovin' it is English, even I say it. It just hasn't made its way into the idiom list yet. Wait for it.
I'm lovin' it = I greaty/tremendously enjoy it.