I think most of us would agree that the way properties do upgrades isn't the best, or isn't even in-line with the T&C's at times... Nothing which couldn't be addressed with some training from Marriott Corp.
That said, I'm reasonably pleased with the upgrades I've received over the past 12 months. Would I like more / better? Sure. At the same time, I've never received less than what I paid for. I'm a cheap SOB and you better believe I'm booking the lowest rate I can find, most of the time. Despite this, I've had many times this year where I've been upgraded to suites, including 2BR suites. At the very least, a larger room or view...and I'm just a lowly Gold, going to Plat this week.
That said, I'm also loyal to those properties (and staff) which take care of me. I make sure they know I appreciate them, and they let me know they appreciate my business. Being pleasant and polite goes a long way in the travel business. I've also received some niceties from the airlines, far greater than what my status should grant.