There is a comparison to 2008 that can be made with the pattern of trading so far in 2011. Despite the similarily, I do not see evidence that a 2008 style of crash is about to occur. The market has a mechanism of alternating patterns which look similar on the surface for a while, but produce a much different end result.
For example, many will remember the May-July 2009 Head and Shoulders failed pattern. Traders questioned the Head and Shoulders top during February to July this year, but unlike 2009, the bearish 2011 H&S pattern did complete and follow through this time in 2011.
This is 2011, not 2008, and the similarity can be useful for a period of time, but ultimately each should be treated as a unique situation.
While the current trading pattern in 2011 mimics 2008, the difference this time shows up in the cycles, and it shows in the sentiments. I remember 2008 clearly, and there were not many bears in the summer of 2008. Since summer 2011, bearish sentiments have built up quite high.
The 2008 pattern also reminds that bear market rallies can be deceptively sharp.
The following is the 2008 Crash.