In theory, everything you want to do is provided by the Sony Ericsson PC Companion software that came with your phone.
However, I've had numerous problem with this software, and found it overcomplicated in appearance, when all you want it to do is sync media and backup stuff etc..For example, it never seems to transfer photos because it just sits there indefinately saying it's "generating thumbnails".
I've gone back to managing the contents of my SD card manually, i.e. via Windows Explorer on my PC and backing up photos/videos that way.
You'd think that a company like Sony would get this right wouldn't you !
I just did some web searches and came across the following sync application:
Auto Upload (Sync) Android Camera Photos And Videos To PC / Server
I'd not seen it before and will try it out later.
One thing I do like that Sony provide is the Sony Ericsson Sync service. The phone already has this installed, although you'll need to add it to the list of synced services. Once you've setup you account at the SE website, you can then sync contacts/bookmarks and other stuff (though not media) at any interval you choose. You can add new contacts on the website and it'll sync back with the phone and vice versa. I actually find this works really well and recommend it.
Rooting your phone allows applications to gain 'admin rights' over the Android OS (as it's UNIX based, this is termed 'root' user). This means you can install unofficial apps (not on Android Market) and change the configuration of your phone to tweak things.
I'm choosing not do root my phone, as considering how many good apps are available, I personally don't see any point as I'm able to do anything I want with it already. And as you say, it would invalidate your warranty.
EDIT - I should add that in order to perform a complete backup of your phone (all Apps/Config/Data) you'd need to root your phone to allow the specific backup apps to gain access to the data files. So perhaps it is worth the 'risk' ?
