I went back at 14 weeks for a 2.5 days a week. This upped to 3 days a week when dd was 2. I felt evil, but my employer had taken me on when I was 3 months pregnant, so I felt obliged to go back as early as I could. I found it very easy to compartmentalise baby and work as I had great child care in the form of grandparents and a close family friend, all of whom added something to dd's upbringing. I gave up work when she was 4, after my 4th miscarriage, realising that I wasn't going to have any more babies and I needed to make the most of the time I had with my PFB (Only Born!). I also felt my job gave me little, other than money, and didn't really enhance my life greatly. I traded on Ebay for a while and then I gave that up and became a teaching assistant, a job I love beyond reason.
DD is 12 now. She is, I believe, a much more rounded child for having had a nursery experience from age 2. The time I spent with her, Mondays and Fridays, were Mummy and babyrabbits days and I loved them beyond measure. I still miss em now. I feel like I made the most of her childhood and I try really hard to remember how much fun we had together now she's in that awful pre-teen, know-it-all phase.
Do what feels right for you. Don't take too much notice of the press or what other people think. Half the time we penalise our kids if we don't set them an example by going straight back to work, the other half we penalise them by putting them in nurseries and ruining their chances in life. No-one knows what's right for your family but you. Good luck