I've been using IS for years, and also I run it with Weather Display quite okay.
I use a Spectra 8 card for camera capture, but the drivers only work under XP, so I've had to put it on another box with XP on it, which I use for my amateur radio stuff.
CPU wise, with 3 cameras running it does hover around 20 - 30 % most of the time, and sometimes it jumps to over 50% cpu.
I'm currently inbetween homes, sold the last, waiting to get new one built, so have no cameras running so I put IS back on to the Win7 box that my station is running on (disabled the canvases that were camera ones), and uses very little cpu.
Glad to see there's still a support section available for the ImageSalsa group.