I have iphone 3g, unlocked and jb, 3.0 firmware, recently:
-cydia wont open just goes to load screen and exits
-itunes cant verify phone
-when i restart itunes and it wont even play anymore, unless the iphone is dettached.
Syncing is a no no obviously, so cant add music

what can i do? i do not want to restore and have to jb and unlock again(nor do i know if that will solve it.)

it used to work fine, till i guess i prematurely removed it from itunes(but again just a guess)

Have you got the latest version of iTunes? I don't and I'm having a similar problem in that iTunes just thinks and thinks and stops responding so since j jailbroke the phone I haven't been able to link to iTunes. I dont want to re-jailbreak as that'd be a massive chore.

Wow!

Don't everybody chime in at once! Form an orderly queue, please! One at a time!

I installed the latest version of iTunes and left the machine to think for a long old time and it worked. I understand your problem is a little different but I wouldn't hold my breath waiting for a constructive reply round here.

sighhhhhh........ yeahhhhhhh thx for tellin me, this is lame, and ya latest itunes. any good websites?

Try the modmyi forums.

Have you turned off SSH?

If you have SBSettings there should be a toggle to turn it off and on in there. If not then download the toggle from cydia.

I just had the same problem you had and it was solved by turning off SSH. Oh, and leave it for ten to fifteen minutes without doing anything on the computer or phone so it has time to do what it needs to do. I suggest going to make a cup of tea or a sandwich or maybe read a chapter of a goood novel or take a short walk, that can be very invigorating and can put you in a good frame of mind so when you then return twenty minutes later and see that nothing I have said works you may find the strength you need not to hurl the computer and phone out of the window.

Good luck.