That totally depends on what you want to do with Redis/MongoDB. Do you intend to use it as your primary data store? AFAIK One of MongoDB's goals is to be useful for a lot of things you'd normally use a relational database for. Redis on the other hand has a lot of nice things to handle more specialized cases of data.
I have been using Sparrow since christmas and I really like it. On a large screen, Mail.app just does not look right.
Loving the gmail keyboard shortcuts. Seems like every app I like must be keyboard friendly now: From Things to The Hit List, from Mail.app to Sparrow, from Textmate to vim. I blame vim.