Got the D750i and it is not that bad at all. I know this has been t-mobiled (mobile phone equivalent of some porn star being gang banged) but this is what I have found.
Memory stick
Supplied USB cable allows you to see the phone as a removable drive. Very useful when transferring your music to and fro. Bit slow but in the absence of a reader and bluetooth I am more than happy. Also the fact the internal bus supports upto 4Gb of memory is very good. 1Gb Memory Stick Duo cards are at £87 and with Sony PSP coming round the corner the price will come down and size go up very soon.
Radio
Surprisingly good. Good interface, good sound
Media Player
No WMA support but I think in the manual it said it is available but may be the location of my files that is causing a problem. Good quality sound
Camera
I do not have a digicam as a reference but it works very well in low to good light. Shots in the dark with the flash come out surprisingly well colour balanced. Digital Zoom feature really useful (For all you upskirters out there ;-))
General Interface
Biased here as I am an SE fan but can see how the Nokia users of this world will not like how 'laggy' it is. Fast but the key size and feedback is not as near to Nokia quality.
Bluetooth
Very good. Works well and now allows you to either lock in a handsfree or have the link disconnect when you have finished using it.
Signal Reception
coming from a Z600 this is a lot better. Signal is found in areas where the old SE failed.
Speaker
In speakerphone mode it is very clear and loud. When used as a normal phone the level is somewhat low but still clear.
Games
The games engine seems to be very smooth and quick. Probably not as good as some but the screen is crisp and clear.
Charger
They have changed the connector so it means all the old chargers you have accumulated will have to be sold or slung. But this is a lot better than the old one and will not get disconnected as easily when you have accessories connected.
Other
The fact you can upgrade the firmware over the net via USB makes this a very easy to manage phone. The software provided allows functions that the Nokias have been able to provide such as themes, backgrounds etc.
Overall
Little touches like the camera being available when the shutter is opened is good and when the shutter is closed, keylock comes back on. Start / Stop button on the side of the phone to start and stop the music / radio very useful. My favourite, the light on the camera can be used as a light for when you want to see if there is a boost leak at night ;-). It is a nice size and not too big. Ringtones and setting things how you like is very easy and quick.
I tried to make this not as biased but being a SE owner I may have been a bit partial.
Hope that helps dude
Pummy