As a side note - I've read that Windows people would see the Windows logo in this domain and Mac people would see the Apple logo. What do you see? http://i♥.com/.
From my late-night skimming (I'm saying I didn't really read much - this is what I've gleaned) it looks like in 2005 DNS switched from ASCII to Unicode. The support for Unicode domain names appears to be there in all common browsers. I tested Chrome, Safari, Firefox, and IE and all of them behaved the same way.
It seems like people should have started using symbols for fun. No doubt there are non-US domains that require unicode but I'm just thinking about the vanity type stuff. It looks like Network Solutions briefly allowed symbols in .com domains (£.com and ♥.com) but doesn't anymore. Out of curiousity, I attempted to register i♥android.com at a few registrars and was consistently blocked. I then attempted to register i♥android.ws at 3 registrars and 1 allowed it (GoDaddy). Interesting.
Safari hits symbol-based domains nicely. My version of Chrome hit my play domain correctly but then munged the URL. Silly.
Speaking of silly - let's say that people were using symbol-based domains for vanity stuff or marketing - in both cases, they'd probably want to use the vanity names in social sites. Why aren't usernames allowed to contain unicode? I only checked a few sites and they only wanted simple ASCII. I wonder if there is a reason that I'm unaware of or if it is just easier for devs to not think about more complicated usernames.