I think for me it's just the lack of time to get everything I want to do done. The time spent caring, cleaning, cooking, and shopping for Charlie is definitely over 40 hours a week, so it's like having another full-time job.
It's worth it of course, but in an ideal world it would be great to have an extra 5 hours a day to get things done!
What's the hardest part of being a parent for you? Guilt? Money? Being tired? Your baby's sleeping/eating/fussy ways?