It's one of my long-time favorites. I used to struggle with whether it was usable in the real world, until I spoke to a student named Guinevere, who said it was fine to call her Gwen. I realized it was perfectly usable - just like another favorite, Morgana (I know one, personally).
Frankly, it's a gold mine for nicknames. You have Gwen, Guin / Gwynne, Vera...
Right now, my favorite combo is Guinevere Elise. I'm not normally a fan of Margaret, but it does go well with Guinevere (as Guin's middle).
Please rate my personal name lists:
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/109399www.behindthename.com/pnl/69381/91835http://greens-end.myminicity.com