I won a Titan this past week during a WP7 meetup and I am very pleased with it thus far! I am an iPhone 4S user (Sprint) but there is much about this phone that impresses me.
1. The "feel". It definitely has that "premium" aura about it. Well balanced, solid, yet thin...nothing cheap/plastic feeling about it at all. Very little flex. Not quite up to the iPhone but far ahead what else is out there (haven't held a Lumia yet...).
2. The screen. OMFG. Pictures don't do it justice...just WOW. Huge. Combined with the physical construction/feel of the phone it just feels very "next gen". Text is just so easy to read and everything is well spaced. Love it. On the negative side the colors are a bit over-saturated (makes the tiles really "pop" but when comparing the same video clip running on the 4S the skin tones were not as natural), and the level of fine-detail isn't there either. But that was only really noticeable via direct comparison and the huge difference in size might outweigh that for some people. I guess it would be like choosing between sitting on the couch and watching a top-of-the-line, calibrated 40" TV vs. a decent, middle-ground 60" TV (I know that isn't to scale but I don't feel like doing the math

).
3. Mango rocks! I am constantly amazed at how fast and functional it is. Can just breeze through it all day long without a sweat. I only noticed some minor chug using Office (mostly in Excel, but only when opening something), but nothing at all serious. And I did experience some keyboard lag when sounds were turned on, but I tend to turn them off anyway and the lag stopped when I did.
All told, I love this phone. I was tempted to sell it (after I tried to give it away to a family member...nobody wanted to switch to AT&T :blush

, but I think I am going to keep it. My 4S still does more for me overall (in terms of apps, plus I am a Mac user at home) but the Titan (and Mango obviously) is the first thing that gives me that urge to switch.