I've got £150k in one bond that matures in Jan '09 and I've certainly spent a few nights worrying about that, but finally decided to leave it. As others have said, if HBOS defaults on its obligations to its savers then the UK banking industry will collapse as savers withdraw their funds from banks left, right and centre; meaning we will have bigger problems o worry about !
Over the last 3 months or so I have been closing done various Halifax websaver accounts and moving the money in £35k chunks to other institutions (and a little cash 'under the matress' just in case

)
When the bond matures I will likely move it or break it up unless the turmoil is over for LLOY & HBOS.
Basically I think we need to hold our nerves until maturity and then think defensively for the future.