Although, my cousin was born on my birthday when i was 7yo. We had to share birthday parties for about 6yrs (until i wanted boy/girl pool parties!!) I hated it! My mum and aunty loved it though, coz they split the costs....
In my family, in Feb we have 18th, 19th, 20th and 21st all family birthdays (we have 16th, 17th, 22nd and 23rd friend birthdays too), not to mention the 10th, 16th and 29th (think that's everyone!). I've never had to share a birthday party, but with Liebling coming in Feb I think we have a few people worried - I think a few of the Febbies are hoping for a Jan baby! So long as Liebling don't have to "share" a birthday I'm happy for a Febbie. Just makes Feb an extra-fab month.

However, DH's brother has a birthday on the 17th, and his aunt used to be on the 13th (not Feb, thankfully!), so for as long as I've known the family (until DH's aunt died) they've always had shared birthdays despite over 30 years between them.