However, the OP comes from a strong academic background and Google is quite hand-in-glove with premier universities and research institutes. Hence he already has credibility inside of Google.

His academic background helped him. CS graduates and PhDs are a dime a dozen and neither is enough to make you a Real Googler, but the fact that he had 8+ years of research experience definitely gave him an inside track to the best projects.

I would guess he was hired at Senior SWE (which is respectable; unlike the title-inflated startups out there, it actually is fairly senior) or Staff SWE. The Real Googler Line is somewhere within those two tiers. It's not just about title, but location and project play a role. Most Staff are Real Googlers, some Senior are, SWE 2-3 are not unless they're hired as proteges (which is rare).

What's Google like? Well, if you're above the RGL, it's an excellent place to work. Even now, I'd recommend it. Being a Real Googler gives you free rein to transfer about the company. SWE 2-3 are considered a burden so transfer to a good project is very uncommon-- the first thing you'll be asked is why you didn't wait for Senior before transferring as you're "supposed to", but some projects make promotion impossible because there isn't enough visibility-- while Senior are considered about neutral (will add as much as he takes away in on-ramp time) and Staff are slightly favored.

At Sr. Staff and beyond, it actually gets rougher, if only because you can't fully participate in the Real Googler freedoms if you want to keep going. At Staff you should have full freedom of the castle (open allocation) unless you're in a terrible location; above it, you have less freedom if you want to keep getting promoted, because having taken on an important-but-undesirable (2nd Quadrant; see: http://michaelochurch.wordpress.com/2013/01/01/fourth-quadra... ) project is expected in the promotion packet.

I however am told that it is quite an uphill task to join Google without an already established credibility and get to work with their core set of products.

It depends. It's easier to get on Search at Google than to get on the top trading desk at a bank, but I actually hated that about Google. See, banks and trading desks are conservative and risk-averse and slow to promote, but they're fair about it. At Google, front doors have stopped working, but you'll still see a 26-year-old now and then who manages to politick his way into getting a real project. A Facebook offer helps with that. So it creates the impression that everyone is getting this back-channel advancement, but very few actually are. In fact, I think the only way to get fired at Google (advanced rank culture) is for your boss to catch wind that you're looking for transfer or back-channel mobility.

I used to admire Google, and I hate what the recent (post-2008, if it didn't start earlier) crop of terrible managers has done to it, but even now I'd say it's worth it to try the place out. There are good managers at Google and it's a pretty neat place if you get a good one. You can get on a good project as a SWE 3. It's rare, but it does happen. It helps if you're in Mt. View, if you have other offers, and if you have a good manager.