All this talk about Britain's Got Talent's scheduling... I don't think there's much comparison with Doctor Who really.
What ITV is doing is maximising in the short-term by extending the semi-finals by half-hour each night - more ad revenue for them and the silly theory that Coronation Street needs to be kept afloat by these events. To be honest, it wasn't a massive success last year, even when disregarding the awful Derrick Bird thing.
This short-term mentality is going to hurt Britain's Got Talent and consequently ITV in the longer term - it's not an important-enough show for people to stick around for a results show. People will turn over even if Coronation Street's on - obviously there's a crossover but the results is going to be lower than the performance.
And when less people are watching the results than the performance show, it's time to worry about a show's relevance... it's comfy TV and, like Dancing on Ice, it probably shouldn't have a separate results show (apart from the final in BGT's case).
Britain's Got Talent was scheduled perfectly in '09, and whether it's peaked or not, trying to milk it is going to confirm that it's peaked - but if it's scaled back slightly in the final stages, the show's drop might slow/halt.
Take I'm a Celebrity Get Me Out of Here and Strictly Come Dancing as the prime examples of the theory of cutting back, and take Who Wants to be a Millionaire? as another example illustrating what happens when something's persisted with relentlessly.
Opportunity Knocks was still hugely popular by the time of its demise, and Britain's Got Talent can be the same if ITV treats it sensibly.