I've had a four employers, four 401k's, one horror story.
I moved the first employer 401k to the fourth employer 401k recently. Both big companies with very low fees. I'm leaving that 401k open after leaving so I have a guaranteed income fund and age 55 access. The second and the third employer plans were small companies and those 401k's ended up in my single Rollover IRA, along with my traditional IRA funds.
My second employer was the horror story. A small company that was going to be bought-out. I left. The 401k fees weren't horrible, so although I intended to move it, I didn't get around to it right away. The "smart money" got out of the 401k, then they split the fees to liquidate the 401k proportionally across the remaining "dumb money". So if there's any chance a 401k will be liquidated, get the heck out!