I've taken the Top 5 and Top 25 times in the world per year over the last decade and looked at how the averages shape up. As the data shows, in the years 99-07 the average time for the top 5 fluctuated by no more than 0.31 secs (2003 and 2007) and the average time for a top 25 time by no more than 0.30 secs (2002 and 2007). Then the techsuits arrived and we saw the average time for a top 5 50m Freestyler in 2009 improve by 1.04 secs (4.95%) and a top 25 swimmer by 0.92secs (4.11%). The techsuit led to an unnatural progression in the event and I have tried to look at what the Top 5 and Top 25 times in the world will look like in 2010.
There was consistent improvement between the times set in 1999 and the average times from the years 2004 and 2007 in the 50 Free. However, times in 2007 could still be set wearing full bodysuits/leg suits which we no longer have. I therefore predict that times in 2010 will be a shade slower than in 2007, but faster than in most other years between 99 and 06.
To make top 5 in the world this year I predict you will need to swim around 21.88.
To make top 25 in the world this year I predict you will need to swim around 22.18.
Popov's fastest ever textile mark sits at 21.64. I expect the top guys in the world to get very close to that this year.