With the advent of computers into family life it is sometimes easier to get our eldest to type his messages as until recently writing was not something that he enjoyed. Typing a letter onto a computer is less personal if it is just the name and present details that are changed and it doesn't show the child's developing handwriting (although we did leave in the creative spellings!) but it does get the job done.
Having done our letters and felt proud that they are all in envelopes ready to post I then stumbled across this link on Filth Wizardry about a website where you can generate a font of your child's handwriting. You download a printable template for your child to write each letter of the alphabet (plus the common punctuation marks), scan it in and upload the image and wait for your font which you can then use in all of your documents. As I said - we haven't tried it yet but there are some great examples on the Filth Wizardry post so you can see how it works. I think we will try this for the birthday thank you letters later in the year - so watch this space!