hah! I'm late, too but in case anyone else is ever seeking the same:
I second the recommendation to Barbeque Tonight in Karachi. That is one fabulous restaurant for BBQ, one of the best I've been to ever. Not for ambience, service, or anything else but the FOOD. Definately try the Afghani tikka with Afghaani dried plum chutney, the seekh kabaabs, and anything grilled. that's what's best. I didn't like their karhai (tomatoey sauce based "stir-fry") but they are really a barbacue joint, so go for their specialization. They are very sanitary.
In Islamabad/Pindi I would suggest you take a trip to the Food Street. It is pretty sanitary and meant for kind of middle-class families. Just choose a stall that seems busy (means it should have a repuation for being good and clean) and eat from there.
I'm also late but... I have lots of suggestions for Islamabad: theres a great restaurant I called Khaas, which has fabulous food and is in an art gallery up in F6-3 (St 2, House 1 or 2) theres also a great Lebanese restaurant in F6-3 and Kabuls as mentioned by Salmon is also a favourite of mine. I'm still searching for more great places to visit though, so if anyone has any more suggestions, please post.
this is late but just incase. I used to live in Islamabad but it was 10 years ago so this may be outdated. One of my favorite places was an Afghani restaurant in the blue area (on Jinnah road closer to Attaturk Ave (I belive) on the side of the road farthest from marghalla hills, south I think -- if that makes sense). They had spits of meat outside so if they are still there you should be able to find them by driving down Jinnah. It was popular with locals and had the most amazing lamb so I hope it is still there (they also have brains over rice that people seemed to love). Another Afghani place is Kabuls. I believe is in / near Jinnah supermarket (taxi drivers should know). Its a fun place to sit outside, eat loads of meat, big naans and rice while surrounded by the smoky charcoal and the market. Also, one of my favorites was to just go to the local chapatti shop (should be one in most markets -- ask around) and get stuffed meat or potato paratha and chapattis fresh.
Not much else to do for fun (in public) in Pakistan but eat. Note: No alcohol served anywhere (not even hotels) and don't even think about bringing it in the country as they X-ray your bags.
In Karachi, go to Barbeque Tonight (everyone knows it)--a five story mega kebab and nan complex--very popular with locals/families and an "authentic" Karachi middle class eating experience.
Blood oranges and grapefruit should be in season.
Go for a evening boat ride in the Karachi Harbour where they cook up fresh prawns (not caught in the Harbour)--see if you can find Captain Salim.
If you find yourself in the Rawalpindi Airport, there is a restaurant (one floor up from the main level) which is very pleasant. Had the White Karachi chicken which was delicious.
I may have to consult w/ some relatives, but there are some good, really good, halal-style Chinese places. As well as a plethora of good tandoor, and I recall being taken to a (filthy) market as a child and eating brains for breakfast (to see if I could "hack it"). It was delicious.
As with other countries in that area, it's all about the street vendors/hawker stalls. Sometimes you just gotta follow your nose.
Oh, I'm referring to Karachi here.
I am sorry that I don't have any fantastic chow tips. I just returned from Islamabad, and I was very happy to know that the Thai restaurant in the Marriott was actually pretty good. The service is slow, but the Pad Thai Gong Sod is pretty tasty. I was not able to get out in town much...