Although the new Mercury Playback Engine is by far the most significant new feature in CS5, it does have some other enhancements. Even more video formats are now natively supported, including AVC-Intra 100 and AVCCAM, alongside 10-bit Digital Picture Exchange and XDCAM HD 50, which uses a Long GOP MPEG-2 structure and 4:2:2 colour.
Support for DSLR video has also been improved, including direct compatibility with video shot on the Canon EOS 5D Mark II and 7D, plus Nikon's D90, D300 and D3000. Performance with Red R3D digital cinema files has been enhanced, and HDV can be captured with scene detection, something formerly only available when using third-party hardware such as Matrox's RT.X2. You can import non-encrypted DVD video assets as well, finally. This now makes Premiere Pro CS5 one of the most format agnostic video editing apps currently available, although Avid's Media Composer 5 is running it extremely close.
For those currently using other editing apps, Adobe has made switching to Premiere Pro that little bit easier. You can import and export to and from Avid using the AAF format, and Final Cut using XMP. Initially, this will probably be more useful if you want to use Adobe's other video related tools - Flash, After Effects and Encore - but you might get tempted to switch wholesale after trying Premiere Pro, too.
With a massively altered playback engine, it's not surprising that new filters and transitions are few and far between. However, there is one very important addition. The Ultra keyer, which was available as a separate app in CS3 but disappeared thereafter, now makes a return as a filter. The virtual set system available with the standalone software is missing, but the powerful keying technology is available again, providing much greater tolerance of unevenly lit and wrinkled backgrounds. The Ultra keyer is also accelerated by graphics hardware, so playback remains smooth even with HD footage.