Sky? Actually yes you can...
You can use Cams with Sky under Linux although in all the official forums/chatrooms for the various media center suites (such as MythTV) it is frowned upon to talk about it.
There is FOSS available which sets up virtual tv card devices, the Cam is linked directly to them (with your viewing card in) and then using software the stream is decrypted before sending it to MythTV. This method also allows you to have the equivalent of Sky+ on your computer since 1 Cam and Viewing card can be used for upto 4 tv cards (possibly more) giving you 4 independent channels available at any one time. Of course you need to run the lines from your LNB (the hardware on the front of your minidish) but that is just a case of buying cable and plugging it into the spare ports on the LNB, each one of these lines will be an independent stream. Most people who have had Sky installed in the past 5 years or so will normally have 4 ports on their LNB (some older systems only have 2 and some newer systems as many as 8 since SkyHD and Sky+ came onto the scene).
Ordinarily with Sky Multiroom you would need as many boxes+viewing cards as you want to have independent feeds, so if you have 4 feeds from your LNB you need either 2x 2 Sky+ boxes (which take 2 feeds each), 4x regular Sky boxes or any combination thereof. This is inefficient for a number of reasons;
1. You have to spend a lot of money on set top boxes (even on ebay they can get pretty expensive if you want 4 of them).
2. You need upto 4 viewing cards which until recently meant paying Sky and extra 10 quid for each "multiroom" card per month; although I just found out yesterday that this has been reduced to a £10 per month flat charge for any number of multiroom subscriptions, which I have to say is about bloody time but still expensive.
3. It is totally non carbon friendly. Running up to 4 set top boxes consumes considerably more power than running a single Cam and zero set top boxes.
So yes, you can get free multiroom and free Sky+ (no Sky+ box required). Granted, you lose the Sky+ software (which is crap anyway compared to MythTV) and if Sky change their encryption key (which does happen every now and again) you need to wait a couple of days for the new key to be cracked.
I should add I have never used this system myself as I am a poor student and can't justify the cost of the Cam and multiple TV Cards. However, I have been a MythTV user for several years now and have spoken to many other users in the UK who are using this system with no problems.
It's about time Sky were forced to release their keys to licensed Cam vendors simply on the energy issue alone.