I definitely agree with James regarding native speakers. I don't think separate TLD's should always be used though - check my post here: http://www.seomoz.org/q/multiple-country-site-versions-and-hosting

"If they are only going to be visible in the SERPS and you know they are going to be cut off then they will never see the words after the cut-off point."

That's not always true, but I see you question it later on - I have seen a few examples where people have used long meta descriptions with the intention of the SERPs displaying something different depending on the search made. Here's one I've just found: http://sharkseo.com/whitehat/meta-descriptions/ - though I've just done a search and I got the same meta description ("Dave is a freelance SEO consultant...") for both suggested searches.

If Google doesn't think your meta description is appropriate there's always a chance they'll replace it with something else on your page or the description from DMOZ.

You should definitely not add the ellipsis yourself, what if the length displayed is changed for example? I'd just ensure your first 155ish characters are well-written in a way that entices users to want to click through.

Definitely don't automatically truncate them. It doesn't matter if they're longer than 70 characters, it just means search engines will show an ellipsis after the 70th character on their results pages. Check out the 'SEO Best Practice' section here: http://www.seomoz.org/learn-seo/title-tag

I'd say it has a negative effect on SEO as SEO is also to do with user experience. moneysavingexpert.com used to have a pop-up that appeared just after the site loaded and blacked out the whole of the rest of the screen - I found it hugely annoying; just as I'd started to read the content it disappeared and I had to close something to continue reading. If I didn't already know the site was genuine I would have thought it was dodgy and pressed back or close straight away.

I'm not 100% sure but I think it was the owner of daniweb.com who said she introduced something similar to encourage people to sign up to her forum. Her bounce rate increased dramatically so she took it off as soon as she realised, and the bounce rate recovered. Bounce rate is something that can be measured by the search engines, along with other metrics related to user experience that will be taken into account when calculating the ranking of a page.

Alan's idea, to do something more subtle, is a good one. If it was unique and done really well, you might even get extra links because of it, rather than potentially less links as Matt Cutts suggested in the video Ryan linked to.

Check out the free Xenu Link Sleuth and this post: http://www.seomoz.org/blog/xenu-link-sleuth-more-than-just-a-broken-links-finder

I haven't used it myself (yet), but Screaming Frog could help as an alternative, though the full version is paid. This post compares the two: http://www.seomoz.org/blog/crawler-faceoff-xenu-vs-screaming-frog

Either add the page number at the beginning or remove them completely, yeah. Rand recommended removing them here: http://www.seomoz.org/blog/pagination-best-practices-for-seo-user-experience

In normal paginated results it makes sense to have the page number first for pages 2+ as page one has the highest SEO value - you want to show Google that that is the most important page for the topic term. Adding the page number at the start of the title tag for pages 2+ gives an indication to the search engines that they're not quite as important as the first page. I imagine this will more often than not be the case for forum postings too, though there's always a chance the best content will be posted pages along the thread.

What would be best for the user? I think it's about finding a balance between load speed and content without spreading the content too thinly across multiple pages, and being aware that constantly clicking to the next page can be time-consuming. Think about how the forum will be used - will people regularly come back to read one or two new posts? If so they won't want 40 posts loading on a page. Do users often make lengthy or short posts?

Things like signatures and images will slow the load speed down, so take that into account when you come to a decision. Perhaps make signatures visible to logged in users only, if applicable and possible? While 'content is king' faster speeds do have an SEO benefit too.

It's a balancing act, perhaps start with 15 and adjust that over time when you start to get a feel for the content that's posted.

It'll just look spammy. Exact matching anchor text seems to be becoming less effective anyway, and Google is good at looking at the context links are placed in, so if a Spanish link is inserted into otherwise English text that will probably look dodgy. And if you're targeting Spanish search engines, links from other countries have less value anyway.