Why is it taking so long to pick up my title tags?

Now, I changed my page title 2 weeks ago. Google picked it up and has been using the updated one for a week. Now I check the SERPS it has reverted back to the old page title even though I didn't make a modification back to the old title. I cleared all cache etc, but no go.

Does Google do that sometimes, and if so, why? Well the answer is they have multiple datacenters. Each data center has a different data age...one will see your new page title before the next does.

You can see some variances across datacenters by using a tool like http://dccheck.com/

Where there are also updates sometimes those sorts of tools let you see what is changing, though search result reading requires a good amount of practice and knowing a few keywords (and the sites that rank for them) quite well.

Then I noticed that when the old page titles came back we also de-progressed to the same SERPS as before losing a couple of positions on some keywords.

Is this normal? What does this indicate? Google is making changes to the Irish main DC or what is it? Should I expect the proper DC to come back online with the improved SERPS again or..?

It turned out I was seeing data from different data centers. I would not try to read anything into beyond noting that you are seeing 2 different data centers with different data on them. The algorithms and data sets are constantly changing, so I can't say everything will be the exact same...but generally over time they all typically end up trending in the same directions.

If you hold your mouse over the "Cached" link in the Google serps you'll see in your status bar at the bottom left of your browser just where Google is giving you that result from. So I just did it and they're giving me results from 216.239.59.132. Another time it might be from another datacenter. I make notes on which datacenter I found a certain result in if I'm tracking a site. Hope that helps a tiny bit otherwise if you want to speed up the whole process look into hiring a link building services, by increasing the link the Google bot will visit more often.