Thought my experience was releveant to this thread so i'll post it here.
I brewed my 3rd batch saturday, a Franziskaner Heffeweisen clone. Parshial mash with the white labs liquid yeast. My other two, a Hoegarden clone and a stout, were done partial mash, but with the grain bag method. 1st batch, the Hoegarden clone came out ok, some funky off flavors in a few of the beers but most of them were surprisingly pretty good. The stout is still fermenting but tasted a hydrometer sample and it seems good. Anyway I was very excited because this was going to be my first serious batch. I read everything I could for the last month preparing for this one, bought a huge 7 gallon boiler and built my own mash/lauder tun from a cooler, this one was going to be awesome. Only problem...the ingredients had been sitting in my fridge and cabinet for over 6 to 8 months (long story), and since i've never brewed with liquid yeast I didn't realize until it was too late that the yeast had expired. I tried to throw together a starter (after feverishly googling) which failed terribly. I just said oh well and threw it in anyway, it was too far to turn back.
After about 42 hours of nervous waiting I saw no activity in the bucket. I was panicking about to buy more yeast to repitch, but after reading this thread I took a cool approach and gathered a hydrometer sample. I noticed a small head on the surface which was a good sign, but very small could have been anything. The reading was a tiny bit lower so it was working...a little bit, I hoped. Was still too close to call, we had been drinking for awhile when we took the OG reading so I was still unsure if it was accurate. Tasted the sample and it was definitley a little fizzy so I was somewhat assured, but still nervous.
Followed what I read here I gave it a good shake and the bucket immediately foamed like crazy, foam got in the airlock and leaked all over the outside of the bucket. I cleaned it up and refilled the airlock and went to bed. Next morning im getting 2 to 3 bubbles per second, and the entire room smells very strongly like bananas.
So yea, take it from a worried beginner just like yourselves. Just wait. it's pretty hard to screw this process up, the yeast really do know what to do, just sometimes need a kick in the pants to wake them up.