Reminders. The Reminders feature of iOS 5 is more simple and integrated than my apps, but I already have apps that let me set reminders and make to-do lists, so this isn't exactly revolutionary. What I really like about Reminders, though, is the ability to set reminders that are context-sensitive based on location. If I want to remind myself to pick up a new hammer next time I go to Home Depot, that is a location-sensitive task, not time sensitive. There is no point in having the iPad remind me at 2pm if I am nowhere near Home Depot at 2pm. But, I can set the reminder based on location so it pops up when it matters--when I drive into the Home Depot parking lot.
Safari. The Safari browser gets an overhaul in iOS 5 with two important changes. First, it gets tabbed browsing which will be significantly more efficient than the current mode of switching between browser windows. Second, it gets a new Reading List feature that lets you tag and save Web pages to be read later (and iCloud keeps the Reading List synced between iOS devices).
iCloud. The iCloud service will actually be of particular value for those who use both an iPad and a PC because it will instantly and seamlessly backup and sync email, contacts, calendar events, and documents across the platforms. The service will be very handy, though, even for keeping data in sync between an iPhone and an iPad, and it provides some peace of mind that your data won't be lost even if your iPad is lost, destroyed, or stolen.
There are a number of other changes with iOS 5 and iCloud that will be nice. The AirPlay Mirroring feature will let you stream exactly what is on your iPad display to a monitor or TV using Apple TV, new multitouch gestures will make it easier to navigate among multiple apps, and the Twitter integration will be nice.
From an iPhone perspective, the changes to the camera will be awesome. iOS 5 will let you instantly access the Camera app from the lock screen so you can quickly snap a picture before the moment passes. And, iOS 5 lets you use the volume-up button on the side of the iPhone as the shutter button, which is much more intuitive and less clumsy than tapping on the screen to take a picture.
Will iOS 5 and iCloud change things? Yes and no.
None of these features--with the possible exception of wireless updates that free the iPad completely from requiring a PC--is a game changer per se. I think many of them will make the iPad much more effective as a productivity platform, but none of them fundamentally alters the answer to the question of whether or not the iPad can literally replace a PC and function as a primary computing device.