Howdy, I know a bit about SEO. The key is making your titles relevant and using key words in the articles. If you develop an article on a new streetcar line, make sure you use words and phrases that people will search for to find your article. You also don't want to overload it with keywords - make sure it's relevant. It looks like you're doing a good job already and using the category function for posts is an easy way to associate keywords with your articles.
Also, try beefing up your metadata, especially for images. Wordpress offers plugins to do this job but you can also do it manually, such as by adding descriptive text to images. This also helps make the website more friendly to people browsing with screen readers. Anyone with visual (dis)abilities may also require descriptions of images rather than looking at the image for detail. So there's an added bonus there.
There's not too much to say - most content management systems have a bit of an SEO focus just because of the way they're structured. Well, it's the fact that they are structured that helps. Someone might be able to comment a bit more, but that's a bit of a brief glance got me.
Apologies to any SEO experts if I've mucked this up
I noticed you hurt your Google SEO temporarily with your weekend downtime. I no longer can see forum posts on UrbanToronto. For example, googling "vegata_skyline" no longer shows results at the moment. Hundreds of Google results have disappeared.
Usually, Google is very smart about detecting when a site is down for maintenance, and they still keep search results cached, so hopefully they all reappear quickly. But if you make a SEO mistake, those valuable search results will permanently disappear (instead of temporarily as right now).
This is your SEO repair priority today -- stat! (be careful what you do next)
Loss of Google juice might be starting to occur. Depending on how your users are searching -- in this case, if you look at your Google Analytics, your incoming search traffic might be already much lower to "urbantoronto.ca/forum" (or with an unusually high bounce rate, due to "Not Found") and will be lowered for about 1-2 years if you've already seeing fewer visits coming from Google, since "veteran-ness" of links is extremely important. It's always a good idea to write a URL rewriter that preserves the old forum thread URLs to automatically redirect to the new forum URLs. You may be running out of time to do this.
This is your most important ad-revenue-resurrecting SEO move; if you notice your searches towards UrbanToronto Forums going down at all, this is possibly 90% of the cause.
Google still memorizes the old links for the moment, e.g. in an exact-string search example. Click either UrbanToronto search result, and you get "Not Found". If you write a URL rewriter for old forum URL format to new forum URL format (e.g. .htaccess file or php script etc) you could perhaps resurrect at least some of that google juice since Google keeps broken links for some time. This will more quickly re-rank your page rank upwards somewhat, even for unrelated searches, because those are veteran URLs, some that are many years old and now suddenly 404.
Citation: I run a blog site that earns advertising revenue, and learned the hard way. And "Google Panda" maulings are no fun.