Email. No option that I can find to download headers only, just full bodies, up to a (low) truncated limit. Not helpful when you're in a poor UMTS coverage area (like home). Also, when mail is downloaded to the phone, it stays there until it's deleted from the phone, rather than reflecting what's on the server, like all other phone mail clients I've enountered and which would be more useful for secondary mail access device.
Contacts. Bizzare. Every Nokia I've had since the 7110, back in 2000 has always had enough memory to let me sync my entire body of contacts. No non-Nokia phone I've had ever has. The C975 does not break this rule. Still, in this respect it's no worse than the Z1010. Where it is worse is that at least Sony Ericsson seems to be aware that a single contact might have multiple phone numbers rather than requiring a separate entry for each phone number or email address. Oh, and a contact can not be synced unless it has at least one telephone number - ones with email address only need not apply and one has to manually confirm each disqualified contact.
Nice to have a MP3 player onboard (one thing my beloved 6600 lacks) but not terribly useful out of the box with only 2Mb internal memory and no memory card included.
There's a rubber plug for a handsfree headset. That's handy but it shouldn't be necessary (i.e. WTF hasn't the phone got Bluetooth) and the plug is not attached to the phone in any way (unlike the Z1010) so I suspect we'll be parting company before too long.
On the plus side, predictive text is better than the Z1010 (but still a long way short of the 6600's)...
The more I get to know this phone, the more I'm convinced that this phone is designed for people who simply want to say they have a 3G phone at the lowest entry cost, without regard for actually exploiting the benefits of 3G!