I love what adansmama had to say! I am so with you!
My kids still use them around the house and in the car, because they are terrible about spills. They are perfectly capable of using a regular cup, but they are just so rambunctious I haven't had the courage.
Maybe it's because I'm so accident prone, but I personally use the new straw cups for adults. I have one at work and two at home and that's pretty much all I ever use. I've just cleaned up way too many spills and even ruined a carpet. No thank you! We'll stick with cups that have lids.
I know there is a debate about whether or not using sippys effects teeth and speech. I think the jury is pretty much still out this one. My dentist and my ped (both in their mid to late 30's) agree that it's important for kids to know how to use a regular cup but it is perfectly ok to continue using a sippy.