First time backup to Time Capsule
My first Time Capsule Backup is about 500 gb and the dialog box says it's gonna take about 8 days. Does that sound right?
iMac (27-inch Mid 2011), OS X Mountain Lion (10.8.2), Time Capsule
By wireless, very possible.. do it by ethernet.
You can do incremental by wireless once the full backup is done.
If you are already connected by ethernet.. turn off wireless.. do not have two network paths.
If you have done that, something is wrong. Test files copy speed to the TC, manually.