The contrast determines how 'black' black looks on a TV.
Higher the contrast the more black or solid it looks. Saying that 1:30000 is still very good, anything over 1:10000 is pretty damned good in fact.
Only a couple of years ago the best plasma TVs out there were only 1:5000 or 1:10000 (and they are still very good) - it is like anything wrt technology... buy now, just realise it will be superseded in 6 months time.
Smaller than 40 inch TV... go for HD Ready and save some money.
Larger than that then think about Full HD but to tell the truth, unless you compare two 50 inch TVs side by side, one full HD the other HD ready, you won't ever know the difference.
The clarity of the pic will still be very good for an HD ready large screen - and as it won't be sitting besde a full HD model in your room, the argument is moot.
If you have the moeny to burn, get the very best. If saving 25% is a consideration, then go HD ready!!
Obviously the last line is my opinion, but I am talking form the viewpoint of having both a 42 inch HD ready TV and a 60 inch Full HD TV. Both are very good.
The money you save could be spent on a very nice Blu Ray player... after all Sky digital is still affected by atmospherics so if you intend watching HD DVDs as well, then a good balance between Blu ray player and TV is the way to go... maybe pushing out the boat on the player (in respect of what you would 'normally' pay for a DVD player... Panasonic ones are pretty good round about the £250 mark).