My Preview.app takes a long time to launch. Sometimes upward of a minute, rendering it practically unusable.
This is because it's "saving windows from my previous sessions", although I rarely see any actually show up.
To remedy this, use the following key combo to discard window information when you quit Preview --> ⌘-option-Q
The next time you start it up, it'll be nice and snappy – the way you'd expect it to be.