All things being equal, when is the length of SETI work units going to be 
doubled (to 648k)?
As time passes there are more and more 'fast' (1 GHz +) computers.
Also, the doubling of work unit size cuts the number of work units in 
half -- a huge simplification of database tracking.

It would be nice if occasionally, say once per week -- a tape was run that 
looks in the 2 GHz / 5 GHz region.
The software does perhaps need some rewriting to cope with reception of 
different frequencies.