Silhouette requires a computer to run. It uses the same software as CraftRobo to cut, but you have the ability to download images from Quickutz. You buy the downloads on a card and use them that way. Any True Type Font can be used, which is nice since you can find a lot of them for free on the net or use scrappinfonts.com for more specialized ones. Also if you want to take this to crops/workshops, you better have a laptop since you can't take the desktop with you.
Vista is not supported until July 2007 on the downloads. Supposedly you can still use the software on Vista, but cannot download. I can't even get their software to install. Right now mine is still in a box collecting dust because of this.
From time to time Quickutz offers free downloadable images, but you have to be able to download them right then to get them. Also if I move laptops/computers you have to call them to see if they will switch over you images since they are encrypted.
This is in general why I love the flexibility of my Cricut vs Silhouette. I just popped in the cartridge and I was on the go cutting instead of my Silhouette still in the box after 4 months. I even tried to call their support to get help and was kind of brushed off with a wait until July 2007...well after spending $300 I didn't want to wait any longer. That is part of my fustration.