I've always had a love/hate relationships with local mail clients - especially between Apple Mail & Thunderbird. I've recently given up on them and found it to be more productive with basic, browser-based Gmail (the vim shortcuts are a must - check Gmail Labs).
There is some hope left however - Sparrow is shaping up to be a minimal client for OS X. I've been using it intermittently and I have to say that it's rather nice for a change. Do bear in mind that it's still in "Beta 4" and pardon its dust.
