Lightbulb jokes

I've always enjoyed the series of lightbulb jokes - you know the ones, things like:

How many hippies does it take to change a lightbulb?
- Five - one to change the lightbulb and four to sit in a circle with a guitar and sing about how good the old one was.

How many therapists does it take to change a lightbulb?
- Just one - but the lightbulb must really want to change.

How many husbands does it take to change a lightbulb?
- Only one, but it takes him three weekends and two trips to the hardware store.

How many surgeons does it take to change a lightbulb?
- None - they'd wait for a suitable donor and do a filament transplant.

How many computer programmers does it take to change a lightbulb?
- None - this is a hardware problem.

How many Englishmen does it take to change a lightbulb?
- Change it? What do you mean, change it? It's a perfectly good lightbulb - we've had it for 1,000 years and nobody has ever complained before.

How many members of the government does it take to screw in a lightbulb?
- None - they're too busy screwing the electorate.

And this week I discovered that we have our very own version of the joke:

How many infertile couples does it take to screw in a lightbulb?

(I'll put the answer in the comments box - but feel free to add your own answer if you have a good one.)