If you're using a hosted exchange account, you need the BES solution. The good news is that BES includes BIS and you can use up to 10 regular email accounts plus your hosted exchange account. Unfortunately, the $30 solution will not allow you to use your hosted exchange account.
No worries about security - it's one of BlackBerry's key selling points. Everything is encrypted between your device and RIM's servers. You can choose to enable content protection on your device as well for an added layer of encryption, and you can password protect your device. That will lock it down so even the NSA will have to spend some time to get in to your BlackBerry.
For mere mortals, the BlackBerry is un-hackable.
For unbiased reviews of the BlackBerry OS, best thing is to dig through some mobile blog sites. RIM gets good coverage at:
Boy Genius Report
None of these sites are afraid to call out RIM when they lay an egg, either in a particular application or with an update to an OS that just plain sucks. Doesn't happen often, but when it does they call it like it is.
Coming from the iPhone, you're not going to find a better browser experience anywhere. Safari is the admitted king of the mobile browsers. The BlackBerry browser is rudimentary but usable. Certainly not anything you will marvel at. As alternatives, you can download Opera Mini (good for some online banking sites that don't like the BB browser) and Bolt (just out of beta, and speedy). If the iPhone's Safari browser were a 100, I'd call the BlackBerry browser a solid 80.