Question: Are there any valid reasons to ***not*** rollover a former 401(k) when changing jobs?

I have several little ones that I never quite got around to rolling together - with an upcoming job change, should they all be combined into my new employer's retirement plan? If not, what else might be considered?

Answer: 
I've changed jobs several times and I chose to rollover my 401k from the previous employer into an IRA instead of the new employer's 401k plan. The biggest reason not to rollover the 401k into the new employer's 401k plan was due to the limited investments offered by 401k plans. I found it better to roll the 401k into an IRA where I can invest in any stock or fund.
Another minor reason not to rollover would be to avoid the pro-rata taxes when doing a [backdoor Roth IRA contribution](http://en.wikipedia.org/wiki/Roth_IRA#Traditional_IRA_conversion_as_a_workaround_to_Roth_IRA_income_limits).