[JKT]

The only downsides to the SchubertIT plug-in are:

1. No scroll wheel support.
2. It uses the same engine as Preview, so it is not fully compatible with PDFs of version 1.6 or higher - this means you can't view any interactive media embedded within PDFs as these require support for version 1.8 or higher (iirc).
3. No support for .fdf files (a problem if you work in academia and use Editorial Manager or equivalent software).

However, it is a good plug-in if you really don't want to have Adobe software on your Mac, and it does offer a lot more options than the built-in WebKit PDF support.

Fwiw, Adobe Reader is actually pretty good now it has reached version 9. Much faster to load and a better app on the Mac than it used to be.