I've a family of blackbirds living at the bottom of my garden, it's only this summer I've noticed they seem to walk/run more than they seems to fly, They dart from one side of the garden to the other on foot, hardly ever see them fly.

gawd Brisket I have no idea!
Why do you want to know?

You need Bill Oddie.

No-one needs Bill Oddie

Not even the Goodies?

I have heard the theory that as they pitter patter across the grass they are trying to fool the worms that it is raining so that they will come up and they can eat 'em.

To move short distances, birds would use more energy to launch into flight and land again than waking/running/jumping.

Nobody knows for sure! It seems to be fairly common that smaller birds hop, while larger ones walk by alternating legs. That sort of makes sense: if you are a tiny bird, you won't get very far with each baby step, so it might make more sense to hop to save energy. However there are plenty of exceptions, even within the same taxonomic groups, and some species (raven, robins, blackbirds) move by both methods.
It would also seem likely that the more ungainly your walking gait is, then hopping/jumping would be a more efficient way of moving over a medium (as opposed to short) distance.

Ah! Now we're getting somewhere. I hadn't even considered that some species would both walk and hop. I'd thought it was unique to a specific type of bird.

Blackbirds and little dunnocks(falsly called hedge sparrows,they are of the thrush family) quite ofter walk/skulk around ground level.They hide in/under shrubs.It's to protect them from hawks etc. We have a aparrow hawk that hunts in the area,it was sitting on my garden fence last week,beautiful bird..Cue very jittery sparrows now who seldom feed out on the open lawn.I put the bird feeders on the shrubs where they have cover.Oh and I chase the local big fat black and white moggie that tries to get them.

...or why do birds suddenly appear, everytime you are near?

Why do birds fly at my car every morning whilst I am travelling down the lanes, making me go 'argghhh' and duck at the wheel?  Is it because I have a green car and they think it's a moving tree?  

yes.