Pros: They fixed almost everything they did wrong the first time (Cingular 8125).
Cons: Why no little rubberized strips on the back, like the 8125? I loved that, because I could set the phone on the dash of the car with the charger and it would (mostly) not go anywhere.
Summary: This is the best single device I've ever owned. If you can use a Windows-based PC, you can use the features on this phone. The keyboard is a huge improvement over my previous phones (Audiovox SMT 5600, Cingular 8125); they rearranged the number and symbol keys into a much easier, more natural format. The keyboard is much easier to use than the Treo or Blackberry keyboard, so if you're going to do a lot of data entry, this is the one.
I used to drag my laptop (with all its peripherals) through the nations airports and hotel rooms; no longer. When on a quick business trip, I just carry the 8525. I can log onto the internet (at 3G speed), go to my company's website, download or enter data, and get my work done while waiting for a flight---and then just put it back on my belt. Battery life is excellent (one day of hard use with no recharge will run you all the way down; by hard use I mean near-constant phone calls). 2 Gig card means I can carry some music to drown out the screaming infant or loud conversation in the next row on the plane, without having to drag my IPOD.
I was in a customer's office and he needed to see a particular document; instead of trying to call someone at the office hoping to (a) find someone and (b) get them to fax it, I merely pulled it up on our company website using my 8525; the customer was able to see a PDF of the actual document on the spot. Needless to say, he was impressed; he called everybody in his office over to watch me "do it again". :-)
Cons: email can be tricky to set up, and some bluetooth headsets work better than others with it. One battery-saving technique, "Turn off all running programs", is relatively "hidden"--it's a Microsoft thing, not a phone thing. If you use the stylus a lot as a mouse (as I did on my 8125), you can expect about a year of life on your screen before it begins to have dead spots. Fortunately, the 8525 has the wheel with which to scroll (that's where I wore my old one out, scrolling with the stylus). Also, the reason I have a new 8525 is that I dropped the old 8125, which shattered into a million pieces. Don't drop it.
All in all, if you're a business professional, especially one who travels, this is by far the best thing on the market.