Well, as long as the development request isn't for pixel perfect. Many people outside the control of development see the mockup from Photoshop and completely freak out when it doesn't match exactly. You try explaining that in the long run it doesn't matter, that browser incompatibilities prevent this, and that it will take longer to achieve that. The people "who know" what's needed don't care about that stuff.
Although, a common way to get them out of their "I know better" state is to point out the time factor and how much extra it will cost them. Suddenly they will worry over browser incompatibilities all day long.
The worse are the people that point out that the fifth paragraph on the third page ends with three words on the final line in the mockup but the website version has four words in Firefox and two words in Chrome. I just want to so tell them to just let the text flow its own way, dude. In the end I tell them in a nice way they're being silly.
When you have the ability to define custom fonts, and there's great fonts out there such as Open Sans which are supported by a whole whack of users, it doesn't make sense not to use that hand have a unified look across browsers and Operating Systems.
Note that I never said that it shouldn't be decoupled, or that people shouldn't use their own designs. But if you want people to see your site as you intended, I'd for sure want them to see it with the exact font I choose, not some close alternative.
Funnily enough, it is exactly what I was taught! I'll freely admit that I'm a 'Philistine', when to comes to these matters.
I've always taken the view that you throw the text at an engine and let it do the rendering. If it doesn't look right, the engine needs improving. Manual tweaks fall into the realm of premature optimisation, as chances are the content will change faster than the tweaks can be made.
I can see that beautiful typography is nice to have, but apart from automation, I can't see a way to apply it on a mass scale. Crafted typography is the typographic equivalent of assembly language?
I hope you do test how it looks on windows? I've worked with a webdesigner that often chose fonts that worked perfectly on his mac, but looked really ugly on all windows browsers, since the fonts were unavailable and the substitutes had noticable style/width differences.
Well, it really depends on how the digitization of Helvetica that any particular user has installed is hinted. The Helvetica that comes with MacOS is quite nicely hinted, and will make for a pleasant read at most sizes.
On Windows, however, Helvetica isn't (at least from my experience) as nicely hinted, or at least doesn't play quite as well with Microsoft ClearType. And that's if it's installed, which is less likely on Windows. In that case, if your font stack specifies a fallback to Arial, which is ClearType's best friend, you'll probably be fine.