I check mine with the base attached because it doesn't count against the checked luggage allowance or incur a fee (at least not on airlines I have flown). They give me a big clear plastic bag at check in and add a tag to it like other luggage. Sometimes it comes out with the regular luggage, other times it comes out in oversized. Travelling by myself with a baby, I prefer hauling as few items as possible through the airport and onto the plane.
Mama to H (10.2010), H (03.2013) - our 15wk little guy born too soon, and looking forward to our rainbow due 05.2014. It's a boy!