While we're on subject, I wanted to note that Helvetica makes a terrible body font. Please use Arial instead for your body, as it renders more clearly and reserve Helvetica for text above 13pt. KISSmetric uses Helvetica and a matching bg shadow blur for all of their body text, which makes my eyes bleed. Horrible practice. Avoid text-shadow for body.
It's common knowledge that Helvetica is a better font than Arial, plain and simple. The issue is just that Arial is somehow optimized for screen display (hinting or whatever), whereas most or many Helvetica versions aren't. At least, that's my understanding, correct me if I'm wrong.
I've always suspected you could get around this handicap this way:
font-family:"Helvetica Neue", Arial, Helvetica, sans-serif;
That is, only use Helvetica if they've got the updated version Adobe has put out, otherwise prefer Arial. I know Helvetica Neue technically was created before the rise of the web, but for some reason I expect it would render better. I've never had a PC that had the font installed though, so I've been unable to test this.