What to look for if yeast doesnt appear active...

I brewed up a Sierra Nevada Pale Ale clone on the night of 4/17/08. It's now been just shy of 4 days and I dont see any activity on the airlock. I know that this doesnt necessarily mean the yeast isnt working possibly due to air leaking elsewhere but I want to pop it open and give it a visual examination...

What should I look for? I used the Nottinghamn dry packet.

Thanks in advance.

You should see krausen- the white foamy "head" on the beer. Or, if fermentation has already occurred, you will see a nasty ring just above the level of the beer. That's a ring left from the krausen. Either one of those signs can tell you if fermentation has taken place or is taking place now. While it's open, use a sanitized turkey baster and take a sample for a SG reading. That's the "for sure" way to know where you're at.