Using web fonts isn't enhancement, it's savig you money down the road from having to hire somebody like me to come and fix your site when it's broken on Windows but not OSX because the system fonts are different.
There is such great typography available in CSS now that there's no longer an excuse for crappy Arial and Times New Roman text.
Many web fonts render poorly on some combinations of OS/browser. Old windows + internet explorer and there is a big chance for the cool typekit font you picked to look like crap.
I use and like web fonts, but from a technical point of view I would rather use a generic "font-family: sans-serif" and let the browser do its thing.
I don't think the parent deserved to be downvoted. I wouldn't personally go as far as just using a generic font-family for most projects, but it is blatantly true that a lot of web fonts, even some popular ones from supposedly high-end font-as-a-service outfits, have rendering that looks worse under some conditions than tried-and-tested designed-for-screen fonts like Georgia, Verdana, and the more recent Microsoft "C fonts".
The web design industry, fad-driven as it so often is, seems to be in collective denial about this. It's like everyone waited so long to get some variety into their sites that now they'll use anything that isn't one of the handful of long-standing, widely available screen fonts. Unfortunately, being different does not necessarily mean being better.
(Edit: Just to be clear, the above isn't intended as a criticism of all web fonts, nor any reflection of the fonts shown in the linked examples, several of which render very nicely and show the technology of web fonts to much better effect. I just thought ogig's point that many web fonts render poorly on some OS/browser combinations was a fair one.)
Sometimes it's not even obscure OS/browser combinations--I've seen sites that were clearly designed on a Mac and never tested on Windows, because the text is completely unreadable on Windows 7 in any browser. I'm all for web fonts, but designers have to test them across at least the major platforms.
Sadly, what you describe seems to happen all the time. As an obvious example, it amazes me how many sites continue to use Proxima Nova as a web font. It renders poorly at almost any common size in almost every Windows browser.
One thing that has surprised me with web fonts is that there seem to be plenty of respectable choices available for free from the likes of Google Fonts and Font Squirrel, and relatively few fonts I would even consider for serious work from commercial font-as-a-service shops like Typekit and Cloud.Typography. After years of me telling people that professional quality results need professional quality fonts, the industry seems to be doing its best to prove me wrong.
I suspect the main difference is that the good freebies were designed for on-screen use from the start, while many of the commercial ones are adapted from existing print fonts already available from the likes of Adobe and Hoefler & Co. Unfortunately, many of those designs simply don't adapt well to the lower resolutions and anti-aliasing used for on-screen rendering.
The trouble is, I don't really care why a font on my visitor's screen doesn't look good, and neither do they. The only thing that matters is that it doesn't look good, and in many cases that seems likely to remain the case until much higher resolutions become the norm for all screen sizes. Until then, as demonstrations like the one we're talking about show very well, there are plenty of decent screen-optimised fonts available from other sources, and they don't come with the financial and legal headaches of the rent-a-font services.
Arial is one of the best fonts available on the web at the moment. Sure, it's crappy, but it's sharp and readable on low resolution displays. New fonts are much better designed, but they're blurry and difficult to read at the small sizes used for body text, because there simply isn't enough pixels on your average display.
Once 4K and 5K monitors become normal, we can wave goodbye to Arial, but I get the feeling it's going to stick around for another 5 or 10 years.
Does your Mac's copy of Arial Have the same character dimensions as the copy of Arial on your windows machine? Does your Linux install even HAVE Arial? What font will it render in for iOS? And Android?
Can you guarantee that the Arial font that renders your menu perfectly on Mac won't be broken when somebody on Windows loads it with their copy of Arial?
Can you guarantee from from desktop to tablet to phone the same text will break lines in The same place?
No matter what font you pull in via @fontface, what I was trying to say is that the days of 'wishlisting' a font and crossing your fingers is over. You can't compete with designers able to zero in and tweak letter spacing because their typesetting is bulletproof everywhere.
This is how I make a living, I get paid to go in and fix 'good enough' to turn it into 'profitable'. Of course you have to test your fonts on all systems, but even more so if you're wishlisting fonts instead of embedding them.
So what font displays on PS Vita when you ask for Arial? I don't know either, but I would bet you any money I could tell you precisely what font any of my sites will load with, on any system. Anything less certain than that is amateur.
Or, to put it in a different perspective: suppose Apple and Microsoft decided to ship jQuery with the OS (of some variety, perhaps a unique version not hosted anywhere else) and while writing sites you had the option of using the native system jQuery (or another similar library because that's close if that OS does have jQuery) and then build your site against that, or you have the option of including a specific version of jQuery in your site guaranteeing that the same code runs the same way everywhere... would most of the people in this thread freak out and insist that you always supply your own library so you can guarantee your code will work on every system, every time, or do you imagine HNers would say »hey all javascript libraries are the same, and version number matters little. JQuery is jQuery is jQuery so code on. Gosh think of all the testing you would have to do if you used the same library everywhere” That's the same decision just with a different type of resource.
There is such great typography available in CSS now that there's no longer an excuse for crappy Arial and Times New Roman text.