Chip I'm planning on working until 38 weeks too. Then having a week if leave, and officially starting mat leave at week 39.
I'm pretty lucky as officially I work from home, at the moment I work from the London office 2 days a week, which involves staying overnight as I'm based in Newcastle. But when I get much bigger and more awkward I'll have to refuse those trips and work from home all of the time.
I want to start my mat leave as late as I can, as the plan is for me to have 6 months and then DH to have 3 months after that, so as a couple we have 9 months. Seemed like a lovely idea at first, and we'll financially be better off as I earn more than DH, so with me back at work we'll be effected less when we're paid SMP. However now it's getting closer I'm already dreading the thought of going back to work when the baby is only 6 months, can extend it a bit with annual leave.
Hopefully I'll be able to manage to 38 weeks, I'll be so jealous of this thread once we get into mid March and loads of people are starting their mat leave.