Thank you all for such great help and advice. I greatly appreciate everyone taking the time to offer some advice.
I probably should say that i have had a bad experience with a Sandisk card failing but I guess this is going to happen with any of the manufacturers - none are perfect. The limited lifetime warranties offered on some cards give some recourse from a failure but little comfort when you have lost your photos.
Getting back to the ebay thing. Yeah, I agree you need to be careful but I can say from experience that when you purchase something from ebay and use paypal you have a lot of security in place to recover your money should something not be right - and this I know from experience. I stick to ebay people with very very high ratings.
Anyway, I'm still in two minds over a 32gb card and I'm glad I've been able to read all your comments.
Susy

ebay readily admits that over 80% of solid state memory sold on their site are fakes. Your D300 shouldn't have any problems handling a 32Gb sized card. I'm inclinded to agree with the majority here, regarding how many shots to 'risk' on each card, and I am in favour of 2,4 and 8 Gb cards myself. However, a large capacity card is desirable in some circumstances, in the similar way a large bulk film magazine might have been for film.

oh its grate.i use only 4gb.it will ore helpful when i will go to the tour.
thanks.

A 4Gb card gives me 300+ images which is more than enough for me for a day's shooting and I have a 2Gb card just in case.

32 GB is a pretty big memory card even though you shoot raw although it largely depends on how much you shoot.