Will I be okay for shooting a 4 hr event with 22GB of memory?

I'll be shooting RAW with a Nikon D300s.

Depends on how you shoot, but I could survive on 22GB. My D3 gives me around 900 images on 14 bit RAW for 22GB… 14 Bit RAW images are approx 25MB on the D3

Its sufficient, unless you are doing it in HD

4 GB should be sufficient. You will have to edit the photos later right? Do you really want hundreds to deal with? Only shoot the compelling images - the required shots, some candids, but don't chimp and just shoot everything and hope you get it all. You neither will get everything, nor will you get what's important. Use your eyes and time when you should hit the shutter button - get the decisive moment, not every moment. You really aren't going to want to wade through all that for the winners. If each image is 25M (thank you bluespeed) 4 images is 100M, 40 images is 1000M (1gig roughly), 160 images is roughly 4 gigs. To shoot 160 images in four hrs.time you will need to shoot one picture every 1.5 seconds - that's chimping, not shooting. With 22 gbs you should not only have plenty of picture space, you should have a bit left over as well.

You'd be cutting it close if your habit is to pray and spray. That is, putting it on burst mode and holding down the shutter button, hoping that one of the shots is a keeper. But let's assume that you are a discriminating photographer who waits for the moment to take the shot. In that case 22GB should be fine.