My townhouse was wired for Internet access and an Ethernet LAN on all floors. The LAN used unshielded Category 5 cable. In the loft this cable was within a few feet of the antennas. Internet access was changed in October 2003 to Comcast cable modem from a dedicated DSL line. Data rate was approximately 3 Mbps and reliability excellent. My multiple hub Ethernet junction was located very close to the antenna suite. Only when I was downloading a large file was any interference noticed on my HF receiver.
I used both Comcast cable TV and Dish direct broadcast TV while at this townhouse. Satellite TV receivers were connected on the 2 floors below my antenna suite. I also have the normal complement of telephones, both wired and wireless throughout the house. I saw no interference to the satellite receivers, cable modem nor to the telephones.
I did experience one source of interference that appears unresolvable. I had a large Toshiba color television in my living room. Since trashed for an HD large screen LCD TV. The color burst oscillator generated interference on the 80 meter band at common PSK31 frequencies (approximately 3.580 Mhz).
My normal ham operations were at QRP (< 5 watts) power levels. I have briefly operated at moderate levels of 20-25 watts. Without any interference. I do not ever expect to run full power (100 watts) in this location. Even if my electronics can withstand the power (treated or untreated), the close proximity to my neighbors is inviting complaints. And besides, QRP is fun!!! Check this page in the future for additional results.
In the mean time, I recommend always operating with minimum power. This axiom of hamming is true particularly with attic antennas and close proximity to neighbors.