At Vanguard, only two dozen out of 2, 500 plans it administers are offering the conversion option for 2010.

FORBES: Roth Conversions In 401(k)s For Real In 2010

He says a lot of big employers and record keepers felt it was too late to offer the in-plan conversion option this year.

FORBES: Roth Conversions In 401(k)s For Real In 2010

For starters, the majority of defined-contribution plans haven't added the Roth 401(k) in-plan conversion option since it was created by a federal law nearly two years ago.

WSJ: Family Value: Is It Time to Convert