Power Vision is EVDO Rev.0, which is a little slower than Rev. A but it's not a huge difference like the original Vision (1xRTT) and EVDO.
The pinch and stretch thing is from the iPhone and some folks like that and are interested to know if another phone ever supports it. It's not really a biggie and the Diamond has it's own methods for zoom that work fine.
It's really very hard to decide for someone else whether they should choose a BlackBerry or Diamond. They're as different from each other as you can get. Some folks love touch screens and others can't live without a good hardware keyboard. Personally, I'd go with one of each, but most folks don't need or use as many phones as I do.
BlackBerry is certainly less sexy and the screens aren't as interesting or fun to interact with/look at. But BB is generally rock solid and stable. HTC does a good job, but WinMo overall isn't as reliable as BB. Not that they're disasters, but you do need to reboot every once in a while. The Diamond, being cutting edge, will have its growing pains.