On dust separation, just about anything is better than nothing. I like the Thein baffle separator ( http://www.cgallery.com/jpthien/cy.htm
) for a quick and dirty solution. If you want to go for an 'ultimate' solution look at the http://www.billpentz.com/woodworking/cyclone/index.cfm
web site and read..read..read ... He is all about your health in the shop. He has a design spreadsheet to help you design a great dust collection system that does collect the 'heavy' stuff but focuses on the fine dust that hurts your lungs (Bill has problems breathing from years of shop dust, so this is now his mission in life to help others not have the same fate). Bill has licensed the dust collection to http://www.clearvuecyclones.com/
They are not cheap, but good. Then you need to either exhaust the air from the shop or put it through filters. Wein http://www.wynnenv.com/cartridge_filters.htm
(also sold through Clear Vue Cyclones) seem to be premium. Whatever you get, get the filters that are HEPA rated or better. Bill suggests 0.3 micron filters. Putting on extra filters means they will take a lot longer to clog.
Yes, I do research lots of 'stuff', and this happens to be part of it...
I have NOT found any empirical data on the best store bought cyclones, but unless you go into a LOT of money, they don't seem to exist, and the Pentz design, and therefore Clear Vue, seems to be one of the least expensive REALLY GOOD designs.
If you are at all concerned about the air in your shop, read Bill's site from stem to stern, then decide for yourself.
Now for the 'do as I say' section... I don't have a cyclone 'yet'. It will come soon after a 'book machine' is finished (under way now). Oh, most cutting of MDF is not done in my shop, it is either outside or in a nearby 'wood shop' owned by my wifes employer.
To vacuum around my shop, I got a HEPA filter for my shopvac. It really helps but has to be 'cleaned' pretty often, but there is a lot less fine dust in the air. But this isn't enough for everything, and yes, as I get a new shop area done, I want to build a Pentz cyclone. But a Thein may be in store to begin with, then put the 'effluent' through a HEPA filter.
Oh, on the Pentz site he does talk about 'conversions' of dust collectors, and power needed, etc. Basically to improve things, use a good filter, not a 'filter bag' (many bags are 5 micron, the 'better' bags are 3micron. You still need 0.3 micron for your health.) The power needed needs to be enough to suck in all the fine particle air for about a foot or two (I forget the exact number, depends on the 'tool') around the air inlet, and it needs to move fast enough to keep everything suspended in air. Bill's formulas and tables will help figure out what you need.
Overall, IMHO, do the best you can do as soon as possible, and upgrade whenever you can (but don't wait very long) seems to be the best reasonable advice I can find.
I hope this helps someone.