Catalyst Theme is one of my favourite builder themes, and if you’ve visited many marketing sites you’ve more likely than not encountered Catalyst without knowing it.
Custom layouts can be created for individual pages and posts.
Control over layout, typography, color schemes, site width and padding, footers, etc. These are all changeable via drop-down menus.
The ability to give different pages and posts their own header (not many themes can do this with ease).
Custom Widget Layout
Numerous skins and ready built custom layouts (skins are a weak point, they’re not the best looking out there)
Squeeze pages can be built quickly and efficiently
License for unlimited domains and free lifetime upgrades
I like Catalyst a great deal as a builder theme, and if you want to design your own sites it’s a strong contender. The (at time of post) free upgrades and unlimited domains license may be a deciding factor for many people.
My one negative is that the skins are not very good, so if you want a good looking site out of the box, either Genesis or a theme club membership at WooThemes may be better directions to look into.