@tomharry2: I think when you're viewing the phone in Windows Explorer there is a folder for the memory card with Music, Pictures etc. inside - just make sure they're in there. This is from memory, I haven't got a Windows machine to check.
@belleville: The software is good, the phone is nice and responsive. E-mail client seems to work fine, I use it to check about 4/5 POP3 accounts. Never sent one through the phone though. The built in browser is OK but Facebook etc. are reduced functionality mobile versions. Not sure if that is Vodafone sending the pages in that way (seem to remember choosing to have an 'optimised' version of the internet or something when I first got it) or if it is just the browser not being able to display the proper version. Fortunately Opera Mini installs and runs.
I do, however have a bit of trouble accessing Facebook at times - after logging in and clicking on something it will often say 'Loading 0/12KB' or whatever but never load. Don't know if that is Facebook, the connection or the phone not having enough RAM or something. The other sites I have used in Opera have loaded OK.
I like the way you can use the phone as a 3G modem through the cable or bluetooth - that's very useful.
There's a Google Maps and eBay application installed too, I have used Google Maps and that's good, never really tried the eBay one.
The camera is OK on the 810 but not startling. Most other would outperform it - there's no flash or anything.
The 810's buttons can crack - the bottom row of buttons on mine have cracked into three separate ones. I think if you press down on the slider when closing the phone it scores lines into the buttons, then they weaken and eventually crack. Mine still works fine, though others might not have been so lucky.
Two other downsides are: I hate to delete text messages so tend to store them using the folders feature, and I'm always at the 500 message limit. I think you try to move messages, it creates a copy then deletes the original. I've lost 5 or 6 messages in the past when moving - they either disappear or texts over 160 characters lose some of the message. That might be because I'm always running up to the limit.
If you copy a picture onto the phone to use as a wallpaper from another camera, sometimes it won't show. That might be because I'm copying from a 8.2 megapixel camera at top quality, I don't think the 810 has the memory to cope with it. Same goes for if you take a picture on the 810's camera at top resolution and try to use the edit feature on the phone, it sometimes says 'Unsupported resolution'.
Using it with BluePhone2 (software that you make calls from the computer, sync SMSs and phonebook, etc.) on the Mac makes the phone restart when you use certain features.
It sounds like a lot of downsides but unless you're using it with BluePhone2, copying massive pictures or store text messages, it's a good reliable phone with good battery life and is feature packed, especially for the money. I've tried to replace it twice (once with an LG Shine to use with BluePhone2, and once with a Samsung Tocco that I got as a contract upgrade) and I keep going back to the 810! Any more questions, just ask.
I wouldn't mind an 830 myself, seems to be an updated 810. Hopefully with some more memory and a couple of bug fixes.