on my 2008 mb, for whatever reason i'm not noticing the same slow-down that i would notice when time machine kicked in. i wonder why that is? powering up the USB drive maybe? during the initial backup there was some slowdown and i noticed more skipping while streaming a movie to my PS3, but otherwise i don't notice the backups. and it's even faster on my MBA. on the macbook i often unplugged TM while working because it slowed my computer down a bit and annoyed me (i know, unplugging it while actually working w/ important data might not be too wise) so i worried about time capsule but those fears were obviously unfounded! i do however have perceived slower wifi connection, need to do some benchmarks to be sure though before i start whinging about that. bottom line though - time capsule might be my new favourite apple product!