When such a beast actually does arrive at £1/W ($2/W) retail-ish, then I shall have the entire east roof of my house covered with it grid-tie (maybe a little space left for some solar hot water). Assuming we're still at our current property.
This time I'd need planning permission, and there is a little bit of shading especially in winter from a tall tree 20m away to the south east, but for those prices, and with a set-up to minimise the shading losses, it could be well worth it. We might even have a feed-in tariff by then.
Rgds
Damon