Griff,
What dire things happen if I do delete them all?
I've been clearing out my Event Viewer for ages. First I copy a filtered "error" report (hi-light, copy n paste to txt) then I run a batch file I found a good 18 months ago. Gives you a clean slate to look at. I can't remember where I found the batch file but this one is (nearly) the same. Not saying that they delete the files, just clear your event viewer.MS won't let me delete the .evtx files.
I tried and I tried, but to no avail.
Oh, I know. Create a live linux CD (I recommend Ubuntu or knoppix) and boot into that. Then delete the files from there.
Disclaimer: I am not responsible for anything bad that happens as a result of my advice.
I've been clearing out my Event Viewer for ages. First I copy a filtered "error" report (hi-light, copy n paste to txt) then I run a batch file I found a good 18 months ago. Gives you a clean slate to look at. I can't remember where I found the batch file but this one is (nearly) the same. Not saying that they delete the files, just clear your event viewer.MS won't let me delete the .evtx files.
I tried and I tried, but to no avail.
What?Still waiting for MS to add a "clear all" capability to Event Viewer.
That's why I use it!!Makes my life simpler when doing testing and wanting to clear out all of the old garbage.

The .event files are the files that are used in conjunction with the event viewer. They should not be deleted. If you have a problem you will need them to solve it.
For Vista and Seven
Working with Vista’s new Event Viewer