I find that behavior pretty refreshing in a world that sometimes feels about as demonstrative and friendly as a lump of concrete. I get the urge to give these expressive people a reassuring hug.

HOWEVER...

People who are extremely friendly, with everyone, all the time, may face two consequences:
(1) It looks like they're not really paying attention to people sometimes. Hi, I'm having a horrible day, I just explained this, why are you acting like it's all sunshine and rainbows? Am I not actually here?
(2) I can imagine that sooner or later people assume they're being flirted with!!! If you don't want a flirty response back, please, back off the uber friendliness just a bit. "Onwards honeybunch darling" within two seconds of first meeting me might incline me to think there's more than "Hello" going on.

So it is kind of refreshing to me, but it can also get as confusing as people who are always gloomy, grumpy, stone-faced, pushy, or severely reserved. There's a time and a place for everything I guess.