Bitcoin sent to a defunct address - what happens to it? I got the address for my account on a site and wrote it down. As I had had a huge hassle buying my bitcoin that morning due to problems with the vendor's site (and which they denied was at their end for 3 or more hours, nearly drove me spare) I was flusterred quite badly.

Anyway, for some reason that is still not apparent to me I clicked on a button saying "generate new account". However, as the site kicked me out due to poor connectivity and it flagged me that "your request could not be processed", I sent the bitcoin off to the address I had written down.

Some hours later I went to the site to check my balance...my funds were not there. There was A NEW ADDRESS for sending bitcoin to in my account details.

So, it would appear that I have sent my bitcoin to a valid address that is now redundant.

What will happen to my bitcoins? Will they bounce around for a few days before coming back or will they just disappear into the ether?
If the address is valid then the bitcoins will stay there until spent.  If you don't have the private key for that address they are now unspendable.

However, in general Bitcoin uses addresses in a different way to that which might be considered immediately obvious.  An address is generally considered a single-use item and as such it is entirely possible that your wallet contains the private key for the address to which you sent these coins, as well as any other addresses which you might have created.  Take a look at your wallet to see if it is present.