From what I've experienced, I believe it only asks for their name if they don't appear in your contact list.
...and only if you have call screening enabled. You don't have to. My clients found it took too long to get to me so I shut that off.
I use GV for a few reasons.
1. I love visual voicemail. I love never having to call in to get messages. Yeah the transcription is so-so, but I can always listen if it doesn't make sense. The play button is RIGHT THERE on my phone.
2. I get Google voicemail alerts from the top bar - forwarding to SMS was redundant, I don't do it.
2. I wanted to kill my business landline - it was costing me $70 a month.
Calls to my business number now go through Google Voice and they ring my home phone and mobile phone (both) during the workday and after hours and weekends go straight to voicemail. I can change this behavior - what number to ring and what days and hours to do it - at anytime.
I have GV set to show me caller ID for the caller (not the GV#) so I can see if I want to answer or not. If I am home, I answer on my home phone - incoming calls are free there, of course. If I want to send it to VM, I do that with my cell.
I now get an immediate voicemail alert on my cell phone when a client leaves a message. After hours when my phones don't ring at all for business calls, I also get an immediate alert, which is a lot faster than before when I had to sit at my desk and think to check my voicemail from time to time. Which I never did on weekends anyway.
If I call a client on my cell, I use GV to do it. So that's the number they see. Making personal calls I use my VZW number.
3. I have one voicemail greeting for business calls and another one for personal calls. I can give each person a different one if i want, but so far two suits my needs just fine.
While I'd like to ditch the $20 extra a month I pay for messaging, I don't think I can, yet. I like Handcent, for one. And I already am saving a lot of $ having basically ditched my business landline.
I don't use GV for personal calls or SMS - just for voicemail and work calls.