Danny Sullivan had early access to the feature, last year, but as he notes, it took two weeks to port the number, as opposed to the one day Google says it takes now. The faster port doesn't remove the warning we gave yesterday: it will terminate your current service, possibly attracting an early termination fee from your carrier, and you will have to establish a new line, and connect it with your phone. Of course, you don't have to establish the new line with the same carrier, if you don't want to, as Google Voice will the old number that your friends and relatives know and call.
Google Voice allows callers to dial that number, and GV then routes the call to your real phone (or multiple phones, and even landlines). It's when you return or make a call that the advantages of Android are clear.
In Android, you can set up GV to completely take over the dialer. When you make a call, it can either make all calls through GV, no calls through GV, or prompt you every time. You can also set it to make only international calls through GV. The advantage to this is that when you make or return your call, those you call will see your GV number in their caller ID. Otherwise, the native dialer will expose your phone's number, possibly confusing them.
On the iPhone, GV can't do this. To use your GV number to return or make a call, you have to fire up GV every time. It's easy to forget, particularly if you look in your call log to return a call. While not that bad, as the call is stil made, it eliminates the advantage of using a GV number instead of the actual calling phone's number.
That doesn't mean things are perfect in Android's GV. Text messaging hasn't seen the same level of integration. If you get a text, you'll get it twice, in both GV and the native app. And you have to use GV to return the text for it to appear to come from the correct number. This limitation exists on both Android and iOS, but we can easily (and hopefully) see it fixed in a future version on Android, but not iOS.
That said, the main advantage to GV is freedom, freedom (now) to port your number to GV, and then point it to one or more than one device. The ability to keep your real number private can come in handy for many, and you can easily block incoming numbers via GV's web interface, as well.
So, should iOS users get GV? Of course they should, more so now that all can port their numbers. It's just that Android's GV is, and unless things change, will always be more powerful and more tightly integrated than on iOS.
Life with a ported GV number sounds wonderful. We haven't made the jump because it would cost us an ETF fee. Keep that in mind, as well.