I just joined this thread and read through the posts. I came across some very good insights and suggestions, and also a load of bollocks. Thought I'd share my 2 pence as well, and hopefully, it will be of use to somebody. I've broken my post into sub sections, so you can read what interests you most.
Good housekeeping rule:
Somebody mentioned that its a good idea to state your area of expertise. I agree that this is a great idea. What I say my not corroborate with whats going on in the IT market, or retail. I encourage you guys to start doing that from now on if you are making job specific posts. My area = Finance & Healthcare
 Frontier Mole brought up a very sage point. Yes, Finance is up $hit creek, and connected industries are also affected. As are construction and IT. Obviously, prevailing conditions have a major hand in this. But prevailing conditions have helped a lot of other areas too, as FM pointed out. I'd also like to add a couple more areas to the list:
- employment linked legal services (severance agreements require independent legal advice),
- consultancy houses (voided roles in companies generate ad hoc expertise requirements),
- restructuring services, ERP solutions (running lean is in vogue!)
Just for your reference, here is the shortage list again, as posted earlier by FM: http://www.ukba.homeoffice.gov.uk/sitec ... mac/uklist
 The issue about coming to the UK is tricky. Few companies (in London anyway) will be even in the hiring mood, let alone sober enough to make hires to the end of the year. To those looking at Finance, I'd say wait at least till the new year. There were a lot of cuts in in the second half of 2008 - myself inclusive - so there may be *a few* opportunities arising in 2009. If you are comfortable in your current role in your home country, and have the cash, I would suggest taking time off to travel to the UK, and network in the beginning of 2009. Touch base with some recruiters and company HR people before coming of course, and have some meetings set up. Often enough, recruiters are quite open to this, and even if there isn't an opportunity available, just meeting them might help as they will be more familiar with you, and will be able to sell you better to suitable vacancies. See also point 3.
 ... with who ever said "only 4 out of 100 job ads are bogus". Not sure if this is industry specific (if it is, its wiser to note that in your post), but its not the case for finance or healthcare. I've been looking at some of the more reputed job boards for these respective areas. They just dont have many posts to begin with. If I've responded to a post that I fit the profile (see caveat below), at least half of them have called back in a week or 2. Not getting a call back doesnt mean they are bogus either - they just may have found someone for the role, and are not keen of taking the time to call me to let me know.
- Caveat: If you dont fit the profile, you have a much lower chance of a response. Yes, this seems elementary, but I know of way too many people who are quite content in just blanket mailing every post they can find. If a post wants at least 5 years industry experience, dont bother applying if you only have 2. If you have 4, at least make the effort to note in your cover letter why you think you'll still be a good fit, and how you compensate.
 ... with those suggesting you wait till the recession is over to come to the UK. Why? Because no one really has the foresight to accurately predict when we really have hit the "bottom", let alone when exactly the economy will have really recovered. If you are really keen on coming, and you got the credentials and resources, make a decision and carry out. Waiting till the smoke to clear and the dust to settle may be too late, and you might not have enough time to feasibly warrant you an extension. Just dont come in Nov or Dec (see point 2)
My 2 pence:
 If you are here already in the UK, NETWORK! I've gotten more leads on jobs I like from colleagues/friends than all the jobsites put together. Plus, a referral comes with a brief recommendation - something that a random email doesn't.
 Dont get discouraged. If coming to the UK really was your dream, keep on trying. Why give up after a couple of failures/stumbling blocks?
 Work some safety nets into your employment contracts. This goes out for those who may be getting hired in the next few months. Make sure your offers come with a couple perks, such as longer notice periods, redundancy pay, relocation, etc etc. Those all add up, especially if you get let go.
 Dont be afraid to cross borders. And I dont mean sovereign ones. If you are in finance, but you have a specialty in the oil & gas sector, consider working for the industry as an alternative. If you are in IT and have been involved in several mergers, maybe look at working for a consultancy house who advises clients on mergers and acquisitions.
My situation (in case you wanted to know):
Got laid off a week ago. Spoke to a couple of connections, and now have a couple of possibilities in the air. Its a mixed bag, with leads in both financial gigs as well as healthcare gigs. Expectedly, the healthcare ones are movig at a quicker pace. If all goes well, I hope to have a new job by the end of January!
Hope this helps, or in the least, promotes more useful discussion.
Good luck to all those out there as well.