I haven't upgraded to iOS 7 for two reasons: it wasn't presented to me yet, and I usually wait until the x.1 release weeks later.
Having been a moderator in some of the world's largest Apple-related forums, I've seen way too many people ask "How do I go back to the earlier release?" The answer is all too painful: delete everything and start over. No one wants to do the tough stuff, but they don't want to wait to see the new stuff, either.
The couple of times I've upgraded before the x.1 release, I was treated to all sorts of problems. However, iOS 6.1.3 isn't exactly working well. I'm still receiving notifications for events in the past 13 hours, sometime longer than that. Rather than fix the difficult problems, most software companies would rather ignore them because they require no money and no work to ignore and fixing requires both.
I suppose when iOS 7.0.1 arrives within a week or two, I'll be on it, 728 MB or not. Does that sound like a lot? The old iOS 4.x releases were 225 MB almost every time.
Sadly, being forced into an upgrade is a problem that you can't stop. This article showed up on MacRumors: http://www.macrumors.com/2013/10/18/apple-sued-over-automatic-ios-7-downloads-to-ios-6-powered-devices/
What's impressive is the unending barrage of comments berating the person who filed the lawsuit. The first two "oh, just upgrade" kind of comments come from people who own the iPhone 5s, which shouldn't have a problem with the latest operating system.
However, I've seen many, many comments about upgrading the iPhone 4 to iOS 7, and people could barely use their phones afterwards. I experienced a similar problem with iOS 5 and my second generation iPod touch. Apple didn't think what they were doing to their own customers.
There should be an option to not upgrade, ever. The person in the lawsuit wanted his phone back to the way it was and $50. That's not exactly a fortune. It's sad to see fanatics jump on such a reasonable person. You'd almost wonder why I stopped being a moderator there.
Update: I upgraded simply because there were 50 outstanding security issues that were fixed. I'm now on version 7.0.3 and the performance isn't great but casual use is fine for my iPhone 4s. iOS 7.1 won't likely be available before the first of the year, so it will be a while before the performance problems go away. I was trying to play a graphics intensive scene in Galaxy on Fire 2 with an add-on pack, and it was extremely unresponsive.
Update 2013.11.08: I've been watching what's been happening on (Mac) OS X Mavericks/10.9 and it's crazy. They're giving away the iWork (Keynote, Pages, and Numbers) applications to anyone on iOS or 10.9, but they've stripped away features in order to re-write the applications as 64-bit code. I'm not sure why this would have any bearing on the functionality of the software, having developed quite a bit of architecture-agnostic software. I can only think that they ran out of time, or they just didn't want to pay the costs of adding things that they weren't going to sell. However, word count seemed a simple function that is now scheduled to be re-inserted into (Pages, I'd guess) the applications. As with Final Cut Pro X, they're going to add things after upsetting customers. Strange Public Relations, yes?