I'll have an 8.5 hour layover at Manchester, any suggestions what to do, arriving @ 2 a.m.? Plus,
How strict is British Air re their "lightweight" carryon regulations?

I would suggest getting a hotel room. There is not much else you can do at that hour.

Flew BA Spring 2005 Boston-Heathrow - flights were full and they were fairly strict about carry-on rules. Did not see them weigh carry-ons but did see them bump people out of line who had larger, heavier appearing bags or multiple bags. Woman in front of me was trying to argue that her big bag was actually a purse - she lost the argument.

From my experience I wouldn't want to take a chance with an overweight carryon - they did weight mine and weren't happy at all that it was 20 pounds.

Hotel definetly!
as for carry-ons, really depends on who's working! some times you can get away with a lot, others i have been unlucky and had to check it in. they are known to use the metal 'bins' at the front to make sure luggage is the right size. you can normally get away with 2 bags - 1 being a laptop/camera bag/handbag, and 1 being carry-on, and then an additional bag or 2 from the duty free shops!

Hotel!
BA can be VERY strict with their carry-on weights. Regular WT is only 13 lbs! Also depends on which class you are flying. You will get a higher allowance as your class goes up. Check the website for each class' weight allowance.
Pack as if they will weigh it. Keep your valaubles separate from your carry-on just in case the case is overweight and they take it at check in.

Thanks to ALL of you for your advice and suggestions.