I'm no longer using the Eris. It was my first smart phone so I'll always have a soft spot in my heart for the HTC Eris but about a month ago I went with the iPhone 4S.
I'm not the kind of guy who gets religious about brands and platforms so it was easy to put the iPhone on my list of choices.
I'm pretty impressed with the iPhone - especially battery life. I usually take it off the charger around 6AM and run it until 11PM and based on the way I use the iPhone, it usually has between 50% and 70% of the battery left. Pretty darn good.
The biggest missing piece for me is Google's free turn-by-turn navigation. It's not available on the iPhone. Other brands are but there is a cost. I haven't tried any of them.
I also wish Swype were an option on the iPhone.
The nicest thing is the consistency and polish of the UI. Another positive is that it isn't pre-loaded with crapware.
Surprisingly the phone part is really good. For some reason I find its operation to be way better than it was on the Eris running 2.1. Why, I'm not exactly sure. It just seems more dependable, intuitive, and less laggy.
As for the glass back, I'd rather it was coated metal. The iPhone on it's own is like a wet bar of soap. A case is an absolute must. Don't even leave the store without a case. I've got a cheap Belkin that covers the sides and the back that takes care of the problem.
The thing is heavy compared to the Eris. I suppose it would be nice if it were lighter but I can't imagine that its weight will ever be a problem for me.
The screen is beautiful. Everything about it is superior to the Eris. Colors, resolution, and contrast are better and scrolling is much smoother. The only way they could make it better would be if the screen went full width of the case. BTW, I took a look at some of the Android offerings and while the physical size of those handsets allow for some really nice screens, I wasn't going to be able to carry them in my pocket and I don't want to start carrying a man-purse so they were a no go.
The iPhone lacks 4G so that was a concern but I hear 3G is easier on the battery and since I have wireless both at home and at work I'm using WiFi most of the time anyway.
Gmail if configured as Exchange is okay. You can read and write emails but the advanced handling just isn't there. Maybe Apple will fix this someday.
The camera is really nice. I hardly ever used the camera on my old Eris. In fact, I've already taken more pictures with the iPhone in a month than I did in 2 years with the Eris. Why? Because the camera produces better quality photos but also because the operation is more intuitive.
I guess the bottom line for me is that I have no regrets. The iPhone fits my needs pretty well. There's room for improvement but if you're like me and not emotionally tied to Android you should give the iPhone a look.