I have been a BB user for the past 10 years. I think about switching to the iphone - i have an ipad and an ipod touch - but I think I would just miss the keyboard way too much. If iphone made a phone with a slide-out keyboard, I would think seriously about switching, but Steve Jobs hates keys and buttons so that is not likely to happen. To me, the iphone (and ipod touch and ipad) are more like fun toys. You will find a tremendous number of applications (way more than BB) on the iphone, a fabulous camera, etc. but the phone is just ehhhh. My husband is hearing impaired and could not even hear when he used the iphone. He switched to the BB torch and viola he could hear his callers.
My BB is an organization tool for me, not a toy. That is what I love about it! BB messenger is probably my favorite thing about my phone. There really is no comparison to other IM apps. I also use Facebook and Twitter, I have a couple of news and sports apps, pandora, weatherbug, etc. It really depends on what you're interested in. All smartphones should work with your email account, as well. I use Outlook for email, etc. and my office uses MS Exchange so this makes email very easy to use. And I absolutely LOVE the fact that it synch's my calendar and contacts.
Oh... and as for the sounds the BB makes when you get an email, that is easily fixed in the settings.