The problem with the "silent majority" this time is that there is no single position for the silent majority to take. We had a united position, "no", to fall back on and people did. Now, party loyalties come into bigger play, and while tactical voting may occur at unprecedented levels it is tougher to turn that into denying the SNP seats.
The current predictions of SNP landslides may be overstating it somewhat, but the fact is that the SNP has a lot of momentum and in many places an apparently unassailable position already, as long as their supporters show up. My prediction in Scotland is:
SNP: 43
Labour: 12
Lib Dem: 3
Conservative: 1
And even this might be optimistic. But we'll see.
Were it not for the fact that the future of this country is at stake, this would be a seriously interesting election from an academic point of view. Still interesting, but in an "oo-er" sort of way.