I was on here about 4 years ago asking exactly the same question. Lovely mumsnetters gave me lots of food for thought, but the comment which really stayed with me was someone saying that it shocked her how easily she could have not had her kids. That she would have enjoyed her life, been happy, and wouldn't have realised how much she was missing out on. We finally decided to go ahead, and have a lovely 2 year old, and that's exactly how I feel now.
For me, it was a real leap of faith: I thought I would like to have my own family - mainly to build for ourselves what I experienced growing up - but the thought of having a young child wasn't very appealing. I loved my pre-DD life, wasn't that keen on other people's babies (I too asked friends with children what the upside was, since I couldn't see it - and never got a good answer! ). But I can tell you now that having my daughter is without a shadow of a doubt the best thing I have ever done or will ever do. This is despite having an interesting, professional career which I love, and having had a fun social life in London, and travelled LOTS (my passion pre-DD). None of it compares to having my daughter.
Of course, there's the caveat which I'm sure haunts you as it did me: that's only my experience, and may not be yours. Not everyone I know has loved it so much.
I think it helped that I'm quite an old mum, and I've already done a lot of the things which aren't possible now, so I don't regret the loss of freedom too much. If there are things you really want to do (like going travelling, or taking a really demanding role) then make sure you do them first. I know you feel it's decision time, but you probably do have a bit of time, and it's better to have no regrets.
The other thing - and this is probably controversial - is to try to think about your own character quite carefully. As a PP said, your character doesn't change when you have children. If you are used to working very intensely, that will help (most people find the first few months very hard, but I found it not dissimilar to the final push when getting a project live). If you generally give quite freely of yourself, or if you are patient, that will also help. If you're flexible, and can modify your expectations easily, that will help a LOT. Enjoying sleep and your own company might seem incompatible with children, but it's surprising how those needs give. On the other hand, if you have time-consuming hobbies which are very important to you, then that's going to be frustrating.
A couple of other things which people told me, which I found useful were:
- Babies don't stay that way for long. Think about whether you want a child, not a baby
- Having children happens around the edges of life. You do still carry on doing other things.
I hope that all helps, and good luck with making your decision.