I've offered this before but it seems the question still needs to be answered: Yes Mjolnir does indeed hit with it's own magical force of impact. There are several Thor comics from the 70's and 80's and 90's which reveal this. Not only does Mjolnir hit with its own magical force, the evidence suggests it hits harder than Thor himself does, i.e. it hurts more to get by Mjolnir than by Thor.

There is a late 70's/early 80's tale where Loki is wearing the gloves that allow anyone to pick up Mjolnir, and he easily batters Thor unconscious with the hammer. (All I remember about the creative team of this issue is that John Buscema pencilled it)

There's a late 80's early 90's tale from the Tom Defalco/Ron Frenz run where Captain America is dog-piled by about 30 Asgardian Trolls, and his only hope of survival is Thor's hammer which is lying on the ground within his reach. Cap grasps Mjolnir, and with one swing of his arm every troll is immediately sent flying off of him with stunned look of pain on their faces. Cap hands Mjolnir back to Thor and comments upon what a fine and powerful weapon it truly is.

There was an Avengers story around the time of the end of Roger Stern's run and the beginning of Walt simonson's so I can't remember who wrote it, but in this story the Avengers are doing some combat training like the X-men in their danger-room and the Wasp's sting accidentally strikes Thor's hand that he's holding Mjolnir in which knocks it from Thor's grasp directly towards the She-Hulk. To save herself She-hulk grabs Captain America's shield and when the hammer hits the shield it still knocks she-hulk on her ass. And this was simply from the hammer accidentally being knocked from Thor's hand, not from Thor actually throwing it with any of his strength behind it.

There was also an early 80's Hulk comic from Bill Mantlo's run with Sal Buscema during the time they had Bruce Banner controlling the Hulk, and in this story (with the Avengers guest-appearing) the Hulk is fighting Thor and they've exchanged several blows already and then Thor lands a blow with Mjolnir and as the Hulk is sent flying through the air he thinks to himself how every time he's struck by Mjolnir it always hurts. (he was able to stand toe-to-toe against Thor trading blows but once Mjolnir is brought into it he's sent flying and definitely feeling the pain.)

Although this next theory is just that, only a theory, a case could be made that one of Mjolnir's enchantments could simply be that it will always strike a powerfully painful/devastating blow regardless of whom it is striking.

Many's the time Thor has thrown his hammer at some supremely powerful cosmic being like Galactus and these being always prevent the hammer from actually striking them, usually with some sort of forcefield. It could be argued they do this because they are arrogant don't deem to let a puny creature that is beneath them to affront their personage, or because if the hammer actually strikes them it will cause them devastating pain.

During Roger Stern's Avengers vs Olympus story-line Thor lands a blow with Mjolnir upon an enraged Zeus and Zeus really loses it, the implication being this blow really hurt him (Zeus).

Regardless of the theory, Marvel's Thor has a long-established history of showing that Thor's hammer does hit with it's own magical force of impact.

"That was my biggest gripe about the Silver Age Martian Manhunter.  His "vulnerability" to fire was so extreme he would literally faint if someone lit a cigarette across the street from where he was walking.  That's just silly.  He should be vulnerable to fire like anyone else, that's it."
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When I had a newborn baby at home, I used to joke with my wife that a plastic bag anywhere in the same room with the baby could be fatal.  "They're like kryptonite to her."

I was purposely misunderstanding the relationship between plastic bags and babies when I made those comments.  Unfortunately, many comics writers seem to treat their characters' weaknesses exactly that way.

Thus, fire is Martian Manhunter's kryptonite.  The color yellow is Green Lantern's kryptonite.  Someone brandishing a gun is Batman's kryptonite.  Laughter is Spock's kryptonite.  Etc.