I'm starting my trip in March 08 by spending three weeks in Hong Kong.
Is this long enough to get a good feel for the place and see everything or have I put too much time aside for this one country?
What's the weather like at this time of year?
Also if anyone is in HK around this time then feel free to send me a message as I'm travellig solo and it would be cool to meet up with like minded people
Well, the weather will be warming up in March, so I guess it should be pretty all right. I've had friends who spent a month in HK, but then again, they were visiting relatives. If you like to take your time with exploring, then I think three weeks is fine. I'm assuming you're including Macau in your trip.
Most people go to HK for quick shopping trips, but there's a lot more to HK than shopping. It offers a fascinating contrast of the old and new, and don't forget to experience the night life.
You might want to check out this site about HK:
Discover Hong Kong
You say you're starting you trip in Hong Kong, so I assume you are going away for a few months? Hong Kong is a fantastic place, and 3 weeks will definitely give to time to get a good feel of the place, but bear in mind that it is a relatively expensive travel destination, particularly for accomodation. If you are on a budget for a longer trip, this is definitely worth considering, as you won't want to blow all your budget in the first three weeks!
Hong Kong is a fantastic and there is lots to see and do. But even I, who would rate Hong Kong as my second favorite in the world, would say that a week is enough to see and do most things.
I would consider going further into China for a bit. Guilin, Yangshuo, and Longsheng are only a (long but comfortable) night train away from Hong Kong and it is well worth a visit. You could easily spend a week there. You could also take a couple weeks to venture into Yunnan and other areas of the southwest, or head to North along the coast to other famous cities.
A week would be lots of time there. As already said, it is expensive. Flights out of Hong Kong are high too-if you can fly out of Macau do it as it is cheaper.