I am currently sitting in a hotel in London after my flight went technical and the crew went over hours, departure time is now set for around 14:00 hrs today, original departure was at 18:50 yesterday, travelling in F what compensation can I expect?

Look up the EU compensation rules. Google search it. The compensation is quite a lot.

If I were you, I probably would have asked to be placed in CX254/CX256, or the next days CX252, or rebook on BA flight that night, which would be gotten in earlier than the delayed flight.

Who paid for the hotel?

From the EU Directive-
* in the event of long delays (two hours or more, depending on the distance of the flight), passengers must in every case be offered free meals and refreshments plus two free telephone calls, telex or fax messages, or emails;
* if the time of departure is deferred until the next day, passengers must also be offered hotel accommodation and transport between the airport and the place of accommodation;
* when the delay is five hours or longer, passengers may opt for reimbursement of the full cost of the ticket together with, when relevant, a return flight to the first point of departure.

Last time when my flight in AMS went tech we got either a shared cab or a hotel. had 15-20 EUR of food voucher. Since my ticket was HKG-AMS-HKG i suppose i could piss around and ask for a refund and return to dirst point of departure...

I don't know if it's a fair statement, because it's just from my own "limited" amount of travel (vs. all the CX/KA flights)...but, I do seem to get quite a bit more technical-related delays / aircraft going tech / etc issues with CX these past year or so, vs. say 2-3 years ago...

CX paid for the hotel as it was a full flight there was total chaos, the CX staff were overwhelmed, and had little or no information.

I am now back home but baggage is well and truly lost!

A few months ago my bag got lost from the States to Hong Kong (LAS-LAX0HKG). for over 20 days they couldnt find it and even issued me a claim chq until one fine day they call saying we've found your bag....so it may take time....but they get around to it.....

I have twice had flights cancelled departing LHR on CX and I always travel in BUsiness class.The service I got from CX was truly awful and frankly speaking they did everything they could to keep everybody at the aiport and did not even provide any vouchers for food or drink and were telling people to go back where they had come from and come back tomorrow, the LHR staff were amongst the worst I have ever dealt with in this kind of situation which I have to say I have had lots of experience over the years with delayed travel

I guess it really depends on where you are huh? I was delayed in Toronto and have gotten great service. Got a hotel voucher, got a $20 meal voucher each for dinner and breakfast. And got another ticket for next day travel.

Then again I was on J ticket so maybe that's why I get good customer service?

If you take time to read my post I was also on J ticket as was many other people, the LHR staff showed their true colours that day and I know very well they did it with the full knowledge that HKG knew what was going on

I believe AA handles CX in LHR !

No they have their own staff

If flight is delayed, the EU directive entitles the pax to "right of care" as stated by kaka, but no additional compensation. If the flight is "cancelled" then there is some cash compensation in addition. But that does not seem your case.

Indeed, hard to understand why you did not ask to be placed on a later CX flight or changed to BA. If you had a F ticket CX would normally do it and full load in F is rare those days (not sure what is the policy for awards).

CX has its own personnel at LHR but they are supplemented by external check-in agents. They must have needed a lot of help from external agents when they have to deal with 300 stranded pax plus their other departing/arriving flights. I allways found CX staff at LHR to be outstanding.
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I remember flying CX back in 2004 from CDG, my flight was delayed, then canceled. Even if we had Y class tickets, they moved us on THAI for direct flight to BKK (was our final destination). But I remember agents telling us not to say it loud because they could not accommodate everyone. Apparently most pax traveling in J or F stayed in Paris for the night... lol

It really seems to depend on how persuasive you are. My partner told them we were expected the following day at French embassy in BKK and that the meeting was important. Sure that it would have been different for a tourist.

When you are flying in F I'm sure they can transfer you on a later flight, BA, or even a flight departing from ZRH, CDG,... Just ask. Even if there are 300 pax frustrated and waiting, they will listen to you because of the price you paid.