[Xperia SP General] ByteFalcon:
1- So far very smooth and great experience. I have around 50 apps installed and so far no noticeable lag or performance issues.

2- The display is pretty good, the viewing angles are not very good but it doesn't bother my much as I'm usually holding my phone straight or have it propped up against something. Other than that the screen is very crisp and beautiful.

3- Like in point #1, no ram issues so far but I haven't tried any resource intensive apps to test it to it's limit yet.

4- Haven't needed to contact Sony so far :D hope it stays that way. Bear in mind their support services might change from one region to another.

5- Personally I'm really enjoying the stock rom so I didn't feel like I need to install any custom ones. There are a few custom roms out there though including Cyanogen Mod

6- There is something that bothers me about this phone but I don't hate it, it's just an annoyance. The phone feels a bit fragile and if you're clumsy or paranoid like me you'll want to get a case for it. The problem is this model doesn't have that much accessories out for it (and no official accessories) so you might have a hard time finding something. I had to order stuff for it online and it was quite costly.

7- WiFi reception is pretty bad, especially when I use it side to side with my other devices. There is a couple of WiFi fix threads on this forum, I haven't read them yet but you should definitely check them out.

8- Camera isn't amazing but it's not bad either. In low light conditions you have to fiddle around the settings a bit first to get a decent shot. Again there's a thread on this forum with users' camera shots to give you a good idea on how good or bad the camera is :)

9- The Galaxy S4 mini is a decent competitor for this phone, it has a better camera and better viewing angles if that's important for you, but it has a smaller screen.

The Sony Xperia ZR is slightly more expensive than this phone but has higher specs and some extra features. Mind that the water proof models have all their ports covered with water tight flaps and the sound on the speakers sound a bit muffled probably also because they are made water proof. (http://www.gsmarena.com/sony_xperia_zr-5421.php)

There are some nice mid-range HTC phones but the new HTCs often have internal battery and memory (no SD card slot).

Overall I'm absolutely in love with this phone. I love the battery life, the screen and the sound (loud speakers included). If you're into gaming this phone performs good and it also supports Sony Playstation's Dual Shock 3 controller which is a nice little bonus. (Hook it up to your TV and play with the controller :victory: )

Good thing you asked this because I stupidly unlocked my bootloader without paying attention and I permanently gimped my phone in the process. Xperia devices have a hidden partition that contains DRM keys. Without them the Bravia Engine and certain non-essential features in the Walkman app won't work. There is a way to back up and restore that partition before unlocking the bootloader. This will keep your phone's full features and warranty intact if you need them.

Check this thread here before unlocking the bootloader :

xdaforums.com/showthread.php?t=2292598