I saw an article at TUAW for an iOS app called PhotoScope. It’s $4.99 in the iOS App Store and I really like it. What it does is allow you to view your entire Aperture Library on your iPad. It supports Tags, Rating, full resolution images among other things. There is a companion app which is free that installs on your Mac which allows for the link to your Aperture Library. It seems to be fast and responsive even with my 200GB library. 

Like sharing in iTunes, your Mac must be awake, though Aperture (or iPhoto) don’t need to be running.

I find that suddenly I rate more photos and do clean up now because I can install my shoot into a Project, then, sitting with the family at the TV or whatever I can use PhotoScope to go through and tag/rate images and more. It has a nice interface and hasn’t had any kind of app crash since I started using it a couple weeks ago. It is designed both for iPhone and iPad though I’ve only installed and used it with iPad.