I use PP5.5 on OSX on a daily basis for work (and used CS4 before that), so I can speak to most of this.
PP can read most common video formats, including Quicktime, AVCHD, RED, AVI (that QT can open, Perian helps), etc. You can adjust the resolution of files once they're on the timeline by scaling, though you're probably better off resizing before importing. You can easily adjust PAR on things after importing, though (Right-click/Ctrl-click on the item in the bin, Modify -> Interpret Footage (Just Interpret Footage in CS4), adjust as desired).
I very rarely ever need to render footage until the final export, my computer (slower than yours) is fast enough to play most effects in realtime. And even on the rare occassion I do need to render, it's as simple as setting the work area I want to render and pressing Enter. Keyframes and basic masking are quickly available through the Effects Control panel or the Effects bin. Keyframes can also be adjusted from the timeline with something that resembles the rubber bands of earlier Premiere versions, but I don't like that interface as much. Titles are available, though rather basic, IMO (I prefer to make my titles in PS and import instead). There's a decent stable of prebuilt effects, though.
For usability, FCP and PP ripped pieces of each other's interfaces off for years. If you've used FCP before X, it's not a huge jump to move to PP. The latest episode of
Film Riot has the host (a longtime FCP user) talking about his experiences moving from FCP 7 to PP5.5.