My vote = The noise the Xbox 360's make is totallyunbelievable!
Even my Dual Quad Core based PC with 8Gb DDR2's is quieter and thats with pretty standard cooling!
I love having it and impressed that M$ have built a worthy product that was WORTH paying for!
The build quality on the exterior is pritty good, but not the same case on the internals, especially with the low quality cooling system they have chosen.
I think if I KNEW how noisey it really was, I may not have bothered.
I use mine mainly within a THX Ultra 2 home cinema and on a 3 meter wide projected Sim2 projector.
I've spent alot time and money in my system, only to be let down by the noise the Xbox 360 makes.
Thankfully, it works well wirelessly, so I'm managed to work around it a little, but it's NOT the answer to hide it somewhere beyond sight, as it makes it difficult with such KooL games like Ravin Rabbids (top game) as the camera won't work on pritty ANY extenstion I've tried!
I would say a close second is the media support! Althought I'm loving the stacks of WMV HD's about, they stil glitch and also means alot converstion with software for other formats.
One thing I think is VERY sad which ALOT of people have ignored! The Xbox 360 can NOT reproduce or pass-through HD audio signals! Very sad and not in my good books for that!
If your not familiar, signals like Dolby HD or better DTS true will NOT play through the Xbox 360 as it should. M$ have chosen to downsample the audio, into Dobly Digital 5.1Ch and thats it!
Try running anything beyond that and it will just down sample it! It's a huge shame and impressed with surround within games (Crackdown, Call of Duty etc) but for movies (mainly audio) it sucks!
OK... so it makes up for it visually (impressive HD visual) but whats the point of great image and poor sound!
I saw a few adverts plastered around (whilst on my travels around our little rock we call earth), stating the Xbox 360 is an all-in-one entertainment system. True, but it's like those cheap nasty all-in-one DVD, VHS and TV's you get. Does the job, but definetly not great or even near Pro Home Cinema!
I'd be happy to pay an extra £100 GBP for a total silent Xbox 360... but thats just me I guess?!
PS . This is all based on the standard 20Gb Xbox 360 as I'm still wondering if the Elite is even worth the effort... very little difference I'm sure and why HDMi I have NO idea... VGA and DVi are SO much better!