Contraceptive Sponges - Opinions? Has anyone used them?

I noticed these amongst the options for birth control listed on Planned Parenthood's website. Does anyone have experience with them?

I can't do hormonal birth control, and while an IUD seems cost effective, I'd prefer to start with less invasive methods.

I was looking at trying the sponges. Thoughts? Has anyone tried them? Are they hard to use? Have people found them to be effective?