I've been using Adobe's Type 1 version of Gill Sans for a number of years on all my presentations. Because of the conflict / headache with Apple's Gill Sans dfont installed, I finally bit the bullet and spent $300 to get Adobe's OTF version of Gill Sans (called Gill Sans Std). I had read that the font is exactly the same (just a different name to do away with font cache conflicts). Well, it's not really exactly the same. I notice an issue with line spacing as I was converting my Gill Sans Type 1 presentations to Gill Sans OTF. After converting to Gill Sans OTF, I have to reduce the line spacing by about 2 tenths (in Keynote) to get the equivalent look.
Is this "normal?" There's a change in line spacing from Type 1 to OTF?
Any suggestions of compatibility Adobe makes regarding Type 1 and OpenType CFF versions of the "same" font apply solely to the Type 1 versions of fonts previously sold by Adobe. Adobe has neither tested nor can make any assumptions about the degree of compatibility between Apple's dfonts and Adobe's OpenType CFF fonts.
Even with Type 1 to OpenType, Adobe does *not* guarantee identical text flow. See my blog post for more details: http://blogs.adobe.com/typblography/2005/12/type_1_to_opent.html
That being said, there are two things to note:
1) For fonts that Apple has been shipping since the 90s, such as Helvetica, Times, Courier and Palatino, there are reasons to think they were trying to be compatible with the previous Type 1 fonts. No guarantees, but odds are good.
2) For fonts that Apple added with OS X and later, if they have the same trademarked name as fonts Adobe ships, the odds are pretty good they were both licensed from the same source, and they have a fair chance of having compatible metrics for text setting. But again, no promises.