I found some wooden hearts on ebay and soon realised that any kind of pen bled all over the place! So I decided to use a wood burner (also an ebay bargain) to write the names on.
It was a little tricky to begin with and a few hearts became 'practice' hearts. Once I got used to how much the pen would burn the wood and how heavy to press, it was just a case of keeping a steady hand.
I would say you need to be happy with your own handwriting (or know someone who has good writing). However, you could print off a script and use the backwards tracing paper trick and then follow the line if you weren't sure.
I am really pleased with the result and will be attaching them to fabric hearts (will post soon). However, I do hate all of my guests with names over 6 letters - selfish!