We got one because of poor picture quality from our cable. It seems to help. We switched from cable internet to DSL because the cable internet was unreliable (DSL wasn't available when we first moved into this house, now it is). The amplifier is before the splitter, so it was fine for the internet connection.

Motorola makes a broadband signal booster amplifier (PN 484095-001-00) for this application. Search around on the web for best price. It is probably best to take your internet cable connection prior to the booster since the internet connection requires bidirectional communication. There is a good description of these issues in the attached link.

Here is a link that might be useful: Structured wiring