If the network hashing power is constantly increasing at 10% per 2016 blocks, those blocks will on average take 10% less time than 10 minutes, in the long run.
If this is what you're saying, yes.
If this is what you're saying, yes.
To quantify that.
At the end of October 5, 2011 (UTC), the block height was 148,231 blocks.
At the end of October 5, 2012 (UTC), the block height was 201,987 blocks.
So in the past year, there was 53,756 blocks.
This was a leap year so there were 366 days.
So block generation was at the rate of 146.87 blocks per day.
There are 1,440 minutes in a day.
So each block took, on average, 9.8 minutes over the past year.
This is the hash rate (green) and difficulty levels (red) over the past
- http://bitcoin.sipa.be
As you can see, even with the difficulty rate rising more than 100% over the past year, it wasn't enough to have a huge effect and blocks were still yielded pretty close to the ten minutes per-block target.
[Update:
Here's some raw data from the difficulty adjustment periods with a column seconds populated (2011 and 2012) so the computation can be made to tell how many minutes each block took for each difficulty level.
- https://docs.google.com/spreadsheet/ccc?key=0AmcTCtjBoRWUdHVRMHpqWUJValI1RlZiaEtCT1RrQmc ]
