It's not on to try to explain all of the massive swings from Labour to the SNP by saying that it's Lib Dem voters who defected. The landslide is simply too massive. Glasgow is a case in point.
What is clear is that in spite of all the hand wringing and greetin' when the SNP won last time, they've shown that Scotland can deal competently with its own affairs, and that it can take the course of action that it sees fit, and that will be appreciated by voters. The SNP are making no attempt to hide the fact that there are tough times ahead, but the fact is that the people have heard how they plan to tackle the crises and they've mostly liked what they heard, even the sacrifices (e.g. pay freeze) that have been proposed are accepted. Business leaders also like what the SNP says and have been doing.
Not everybody is happy of course; it's never the case that everybody is, and even though Salmond has come in for criticism both here and in England (over the release of the supposed Lockerbie bomber, for example), people appreciate the way he stands up for his principles. The SNP government, unlike the unionist (apologies for) politicians, don't need first of all to be subservient to their masters in London.
I honestly believe that the flying visits (hurry up and let's get away) by the Westminster masters of the three unionist parties swayed many people away from those parties towards the SNP, as disillusionment with the whole idea of union (which the Scottish people never voted for) continues to grow, and rightly so IMO.