I'm not sure how long the app will survive, but I've checked for the most part it's working - including with AirPlay. And the list of channels include:
BBC One
BBC Two
BBC Three
BBC Four
Channel4
Channel4+1
Channel5
Channel5+1
ITV1
ITV1+1
ITV2
ITV2+1
ITV3
ITV3+1
ITV4
ITV4+1
E4
E4+1
More4
More4+1
Film4
Film4+1
5USA
5USA+1
5*
5*+1
CBBC Channel
CBeebies
CITV
Dave
Pick TV
Challenge
Quest
Yesterday
Really
Showcase TV
BBC HD
Eurosport HD
Eurosport2 HD
Cinemax HD
History HD
National Geographic HD
Sky Movies Drama Romance HD
Sky Movies Modern Greats HD
Sky Movies Thriller HD
Sky Movies Sci-fi Horror HD
Sky News HD
Sky Sport 1 HD
Animal Planet HD
Comedy Central HD
Bio HD
Disney XD HD
ESPN America HD
MGM HD
National Geographic Wild HD
National Geographic HD
Note, there is no additional/subscription cost.
UPDATE: Even though the app is still available (and ironically sitting on top of the paid apps list), it is no longer working. Save your $0.99, don't buy it.
Whether it's illegal or not, the app will be removed from the store (it's only a matter of time), and you can bet Apple will release a firmware update that will block features from this app from working (like they did with FlashLaunch - awesome app that gave us iOS users an easy way to turn off/on bluetooth, wifi, etc. like on the Android).
As much as I love my iPhone, I hate Apple for not making better use of that notifications screen. Put widgets on there for heaven's sake!
That being said, it's only 99 cents. Some of my favourite shows are on E4, so even if it works for a week or so, it's not much of a loss if it suddenly stops working.