How up to date is the Man from seat 61?

I'm my experience it's pretty good, obviously it's not perfect but each page has an 'last updated' link, i.e. here's the Philippines page:

Page last updated: 30 May 2015

with the note

After hurricane damage, these trains were temporarily suspended in late 2012 and are still believed to be suspended as at 2015. It's not clear when or if train service will be reinstated. Please see www.pnr.gov.ph or https://www.facebook.com/pnrailways?ref=bf

Update May 2015: It's reported that PNR hope to get the Bicol Express back up & running by Christmas 2015. Funding has been secured to extend the route all the way to the southern end of the island in due course.

That seems pretty much the case, trains are still suspended. I can't find a source for the Christmas 2015 date but it sounds like the sort of thing PNR would say (not that it will happen).

Given that the Philippines has so little train service I'm impressed he even bothers with a page, let alone keeping it up-to-date.

As Blackbird57 say in the comments, many updates rely on people e-mailing in corrections and updates, so it's a bit like a 'curated' wikipedia. I.e. I'm sure that Philippines update came from a local here, possibly from a non-English news article which is why I can't find it in search.

But a lot of the core schedules and disruptions (particularly Europe) are updated directly from the main schedules published everything six months or so.

Of course, if there's something you want to double check then

Is there still work on the train line in X as of June 2015, if so when will it stop?

would seem completely on topic for this site ...

Mark, the guy who runs it, is a retired ex-railwayman, and is treated by the industry (at least in Europe) as a journalist. He has exceptionally good industry contacts on top of receiving press briefings, as well as a very large number of readers who travel widely and report in, and travels a lot himself (both at company expense, and using his "privs" discount as an ex-railwayman).

Anywhere in Europe, his information is usually more up-to-date and accurate than the official website of the rail company involved. Outside of Europe, it's more variable (he certainly doesn't have the depth of coverage for e.g. China, comparable to "how to avoid the long walk from the Metro at Paris Montparnasse"), but it is regularly updated, and where it is dubious, it will usually say what the sources are and that he's unsure. Take a look at the section about the Zahedan-Quetta train to see how clear he is about uncertainty.

This answer is a little late, but never mind.

Just by looking at the design of the site I would certainly trust it. It's well laid out, not cluttered with ads, and has plenty of information. Also, my browser didn't complain about any security issues.

It has all the signs of a trustworthy site. Good job, @MarkSmith!