I'm pretty sure I have a business account, but I've not yet seen an interface to add additional people to view the stats (googleanalytics and adwords have it, but I've not seen it for adsense)

I'm pretty sure I have a business account cause I went through the hoops of deleting an individual one, and recreating a business one.

I've swapped from a personal to a business account and am unable to see any difference between them

Did you move all your existing stuff into the business account, and if so did you notice any change in your stats during this process? I am a little concerned, as at present the personal account generates a five figure sum and I am loath to do anything that may have a detrimental effect on this. Or would it be best just to leave the existing one as it is and open another business one?

No, the move was quite smooth.
Mind you, I just opened another account in the business name and started ignoring the old account - I didn't do the 'assisted Google move' thing.

Has anyone else used the assisted Google Move? How did it work for you?

I would also like to move to a business account, but it would be too much hassle to replace all the personal adsense code with the business adsense code, since I have hundreds of pages.

Or is there an easier way?

I guess replacing the code would be fairly easily achieved using a find and replace tool in the html coding for the pages.

My AdSense code is all done within server side includes. Change one file and change all the code on every page of the web site that uses it.

mmmmm

But in my situation, I can't just simply change the code on 1 page. I'll have to manually replace the code for each page, which is tedious and tiresome.

Would google allow me to just transfer personal account to business account? Or is there a way I can use the same adsense ID code when I decide to switch to a business account?

First of the only way Google would allow me to transition was to delete the old account, apply for a new account and then go on.

Since I had a website without adsense on it, I had my business apply with that site before I asked them to delete the personal one, I did afterwards asked them to delete the old one (after I had the cheque, the reports etc).
Tip: do it after the old account has enough for a cheque (or a EFT nowadays) so that payment doesn't become a lingering issue.
[Technically out here the business is considered a person, so it can enter contracts independent of its owners, so there should not be a problem anyway]

But in my situation, I can't just simply change the code on 1 page. I'll have to manually replace the code for each page

Check out server side includes (SSI), you really want. It is also one of the ToS that you can make such changes fast if I remember correctly.

Would google allow me to just transfer personal account to business account? Or is there a way I can use the same adsense ID code when I decide to switch to a business account?

I tried, they refused. But you can try to convince them to allow you to do it. Good luck!

The only change I saw lasted very shortly: there was no smart pricing on the new account for a few days so the clicks paid a bit better.

Now the big question that remains: what's the difference: I do not know, I've not found a single bit different.