Well - I guess I'll jump in with my experience. I have had forum web sites online since 1997. I added them to some sites I already had which were, at the time, much like blogs of today. In 2001 I switched to vBulletin forum software on each site from the old UltimateBB (and Darryl Burgdorf's old WebBBS before that starting in 1997). Up until about 2004 it was all essentially a hobby for me and I didn't really pay that much attention to thread titles, or even the sites themselves. I rarely spent more than a few hours in the evening on them. They sorta ran themselves for the most part. In Dec 2003 I was going to take my sites offline and "quit the hobby". A fellow called me and told me how much he would miss the forum he visited, and also told me I had no idea what they were worth. He convinced me to think of web sites as businesses and it was he who turned me onto AdSense. I took my sites out of "hobby" status (no advertisements and all costs came out of my pocket), threw in AdSense, and I had started to see significant income. I re-evaluated what I had. It took me several months but I started going through threads one by one, looking at the content and giving them an "appropriate" title. I've never much been into SEO aspects (I've never done most of the stuff people recommend like "link building"), but this was something that to me was obvious if I wanted search engine traffic. I came to understand that thread titles like "Help! I'm new to this" was not just an issue with SEO (of which even today I do little of), it was an issue of people browsing the forums and doing searches within the forums. But it mainly helps people browsing the forums and their sub-forums. And it makes the forums more "business like". When people see a thread title like "Help! I'm new to this" they're very likely going to pass it by and less likely want to come back.
That was 2004, I was 54 years old and was making enough money to "retire" from working in my field of many years - I was a business systems and standards consultant who traveled 11 months out of the year. Now I have are my web sites. I do quite well bringing in the low 6 figures every year. That said, my web sites *are* a job. I watch every one closely. Luckily, they aren't huge. I have a great group of moderators and they are now helping with what they used to think was a silly thing: We look at every thread title that isn't very clear and retitle it. For all intents and purposes we look at the first post in every new thread to ensure the title reflects the content. It takes a lot of time but my belief is thread titles are like book titles, or news article titles - Every one should reflect the thread content.
It's a lot of work. Personally I think it's worth it.
I will say that here (WebmasterWorld), for the most part, thread titles are usually pretty good. I stop by every day or two to look at the thread titles on the first page. If I see something that interests me I'll open the thread. This thread is an example of my reading it by chance because "Spider Forum Thread Titles" is pretty weird. It's like you took a few key words and threw them in as a title. Forum Thread Titles are very important to me so I clicked on the thread. However, in any of my forums such a short "key words" thread title typically wouldn't be acceptable. Either the moderators or I would have looked at your starting post and retitled it with a longer, more specific and descriptive title. I will add one other thing - My forums rank for "long tails" on specific tech/business topics in searches so thread titles are significant.
I also watch Google (WMTools) for duplicate content (different threads with identical titles) and try to make sure as few threads have identical titles as I can. They can't all be eliminated considering one forum alone has almost 70K threads and another has over 40K threads (small, but profitable niches). But it is a factor. Thread titles here (WebmasterWorld) are typically short so I would think there are lots of duplicate content issues based upon thread titles. I ensure thread titles in my forums are long and varied as I can. Again, I have a wonderful group of unpaid moderators (some of which have been around for over 10 years) who help me with thread titles. I couldn't do it alone and I thank them for all they do quite regularly.
@wilderness - "So are you going to edit the subject lines in thousands of threads and every subsequent thread hereafter? (Rhetorical)" -- I can't say it would make sense here at WebmasterWorld, but I literally did (as I mentioned above) and yes - Every day my forum moderators and I ensure *every* thread has an appropriate, detailed title. And I do mean *every* thread. Cavat: I started retitling threads years ago so if I was going to start doing it today, I'd either have to hire a couple people to do it or just (as was mentioned above) go back a few years. Either way - It's a *lot* of work.
My "inspiration" was that I'm older and thought about all the time I spent in libraries years ago. Go the the card files and you expect to see varied titles. If I was looking for something, the closer to what I was looking for the easier it was for me. On the other hand, it was also the inspiration for me to start forum based web sites. They are a place one can go to find specific information they need with the addition that topics can be discussed (tech stuff often has opinions and such so being able to discuss "definitions", "requirements" and such was (and still is) critical.
Anyway - Those are my thoughts and some of my experience. To me, thread titles are the "soul" of a forum.
I know this is a bit off topic, but as a general comment - The other, and just as important, part of a forum is ensuring every question asked (as much as possible) get's a reply. I don't think that's a problem here, but in many, many forums (especially tech forums like mine) you get a search result and it's a post starting a thread that no one responded to. The moderators and I watch to make sure there is some response, if only a couple of "bumps" which usually get someone to help with an answer.
As always - YMMV.