Ecto does a lot of the things I need it to, like keep an offline archive of my posts, allowing me to construct posts offline, and plugging in nicely to iPhoto, iTunes, Amazon, Technorati, etc. I used it for a few days and then happily paid the modest $17.95 fee to keep it. The only thing I wish it did better was image insertions from a URL. it just doesn't seem to offer as much flexibility as Blogger's own online composition tools in that regard.
I do certainly recommend it, but I'd be happy to hear from you, fellow bloggers, if you have another (Mac-compatible) tool you like better.