We also had a really stressful first 6 weeks. My wee one lost 11% of his body weight and was under 5lb. By 6 weeks I had to top up with fornula as he was still not at birth weight. What we didn't know then but new research was published in March 09 and the medication I was on, it turns out, inhibited the fat supply of my milk so Ruairidh was getting semi skimmed I still managed to breastfeed as well until 15 months. However my friends wee one was introduced to expressed milk and within a couple of weeks was refusing the nipple. My friend broke herself trying to maintain supply through express only but sadly wasn't able to. So really the intro of bottle can go either way.
I agree with Reina, it is so worth it, I can't wait to start breastfeeding again when I have this one and I'm no longer on the offending anti depressants so I'm hopeful we'll not have same issues.
On another note, I think we've decided on a girls name but nothing on boys names at all!