My information/opinion is dated.
I've written a few guides, although it was years ago when we were first able to write them.
The advantage to writing guides is that if anyone ever actually goes and reads them, they'll see stuff you are running and they'll be pointed to your store, if you have one. (Not sure if it points them to auctions if you only run auctions).
Personally in the beginning I think they were great and the work was worthwhile to draw more people to my stuff, but I do not think that is the case now. I'm also of the belief that eBay themselves or through professionals, created their own guides which I think supersede anything we would write.
Unless your goal is simply to educate people, you'll have to look to see what guides are in the category(s) you have knowledge in and are selling stuff in.
I think the new wave of stuff they wanted us to do was the "collections" stuff, I didn't participate in that so far so I can't say much about it.....
PS I went to look at my guides and darned if 18,000 people have viewed the most popular one! Don't know when though, remember it was about 2007 when I wrote them.... I do get the trendy "top 5000 reviewer" beside my id although again don't know if it does any good....
