1) Suboptimal WI-FI performance. On a 802.11g wireless network, connected to an 8Mbps internet connection, the phone can't even saturate the badwidth of the network. Speedtest.net reports an approximate 2Mbps download capacity (EDIT for those who cannot distinguish: 2 megabits, not megabytes). Test it yourself: try to download something from a fast website and try to figure out which is your maximum download transfer speed. You will be disappointed. As a comparative, this means the phone can use 1/4 of the available bandwidth. A SonyEricsson Satio can fully use the available bandwidth, instead (someone told me "tell me a phone that can do it. Now you have one).
2) Stanby freeze: it's there. The phone freezes randomly while in stanby draining all your battery juice. Sometimes happens rarely, sometimes happens frequently.
3) Poor memory space handling: after just 20 days of use from a fresh ROM update, my free memory space on ROM is just 36MB. Without installing big things or hacking anything. Sure, there are fixes produced by the community, log cleaners, temp files deletion utilities, etc. etc. Still, it's a quite a disappointement: it means this phone can't work properly in a "factory state" for much time.
4) "Always on" features: nice, apart the fact in random periods of time the services just stop to download data. The Twitter client doesn't work well. Sometimes you can hear a tweet sound, sometimes it downloads data without the sound, sometimes it downloads nothing until reboot.
5) Poor stability in general: the OS crashes frequently. Less frequently than the first shipped rom. Still it's not very stable.
6) Poor support in general with the updates: finally the SMS stuck problem has been fixed but they spent 3 months for it without a valid solution. The camera fix doesn't hide the fact the sensor is defective.
I don't say this to start a flame, of course, but only because I'm frustrated with these problems. And people, instead of spreading words about them, just pump the hype, including some notorious web sites that have no scope but pushing the hype even further. But the truth is another: this phone doesn't work as expected.