The one last barrier for you using Google Voice full time—number porting—just got knocked down. But should you use Google Voice? Almost certainly yes.
To quickly summarize, Google Voice is like a layer inbetween your regular cellphone/landline and the outside world. It can block calls, route calls on a schedule, record calls, transcribe voicemails, ring all (or none of your phones) simultaneously, send text messages over 3G data (or from your computer), and make and receive free VoIP calls on your computer using your normal phone number. It's really quite good, and I've been using Google Voice for almost two years now with no regrets.
But should you switch?
Just because you can port your number to Google Voice right now, doesn't mean you should do so immediately. Take a look at your cellphone plan. Do you still have a majority of your 2-year contract left? If so, you'll have to pay early termination fees, because you're taking your number and giving it to another provider—even if that provider isn't strictly a cellphone provider.
Also, when you do port your number, you're going to need a new number for your cellphone. (Cellphones need numbers, and you just gave yours to Google Voice. No, they can't share the same number.) This can be your chance to switch providers as well, so look around and see if there's something you want. Verizon iPhone 4 is an option, but I recommend waiting for the next iPhone in June.
Do you really need to port your number?
I understand if you're some kind of professional that has been giving out your number to people for years, or a real estate agent or birthday clown performer that has advertisements up with your number printed on them, but most of you are not. Unless you have a really cool number that you really must hang on to, ask yourself a simple question. "Can you really not just write an email to everyone on your contact list and tell them you're getting a new number?" If you use Google Voice without porting, you can still hang on to your old number and tell any stragglers about your new fancy GV one.
It's easy to get calls...
Let's say you have ported your number to Google Voice, and your number is 212-OLD-NMBR. You still need a new number for your cellphone, so let's say that's 212-NEW-NMBR. You can then assign a bunch of different phones to ring with someone calls 212-OLD-NMBR, like your 212-NEW-NMBR, and your landline, and your work phone. You can even set these individual phones on a schedule to only ring during work hours and home hours, or add one temporarily, like your parents' phone if you're visiting for the holidays.
So, having those neat screening options and being able to pick up any phone you want to answer a call (even your computer, using Gmail.com), is cool.
...but making calls is weird
If you're on an iPhone and make a call like normal, even if your phone is assigned a Google Voice number, it will still appear to come from the number that belongs to your iPhone. In this case, that's 212-NEW-NMBR, the number you just got and don't want to use! But, you can use the Google Voice app, which will make outgoing calls and texts using your 212-OLD-NMBR. Or, you can save what's called a "routing number" or a "direct access number". Whenever someone texts you at your Google Voice number, Google will assign a distinct new number for them. If you want to text or call this person directly from the native phone or SMS app, use this number instead and delete their old number. It's confusing, but it works.