This has been my favorite gift to give moms that are having their 2nd+ baby girl.  After you have the first baby you generally have all of the essentials, so these are a lot of fun for the mom that already has everything!  My second daughter was given these at a baby shower and I put them on her almost everyday for her first 6 months.  Other brands make versions of these (like Target), but they are not nearly the same high quality as Jazzy Toes.  These held up much better in the wash than any others.  The other brands shrink and fade very quickly.  These really look like shoes on their feet, too.  I got more compliments than I can count from random strangers when my daughter wore these.  The grandmothers loved them : )
I don't think I would recommend buying them for older babies (6months+)  Once my daughter hit 6 months we switched to pedipeds and I didn't have a need for these socks anymore.