SeaMonkey released the first stable version. At a first look it looks better than the combination of Firefox 1.5 and Thunderbird 1.5, both are based on the same Gecko generation, so SVG support, tab reordering, global inbox, or whatever you need, but SeaMonkey is faster.
Sure, I can see also some downsides: SeaMonkey does not have pretty pictures, the icon theme is the same old one, remembering of Netscape 4.x days.
It appears the SeaMonkey developers follow a lesson from Firefox branding: they don't want to release the source for the logo graphic, to keep it under control.
I have bad news: such a logo is easy to recreate, here is a very quick job, with a lot of room for further improvements:
Of course, the source is available as SVG