I only recently got into mechanical keyboards. I bought two super modified keyboards from geekhack user TheProfosist back in December '11 and January '12. One is MX Blues, the other MX Reds. I went into buying them completely blind, only having done a substantial amount of reading to figure out which switches would likely be best for me...After using the tester switch, I think I did my homework well because I like what I purchased the best!
Browns - too light! I can barely feel the tactile bump. I feel like if I was using a full keyboard of browns I'd wind up bottoming them out anyway.
Blues - I use these on my work keyboard - lots of typing, emails, number pad data entry, etc. I find the high resistance from these plus the click in the middle is optimal for relieving/preventing any sort of RSI related pain. I hardly ever bottom the key out. I like the way the sound too. Noisy! But nobody has ever commented on it in the office--only that I type fast, not noisily.
Reds - featherweight switch! I use reds on my keyboard at home, where I do mostly FPS and the occasional RTS gaming. I like how they are extremely easy to actuate, and more importantly, keep actuated for extended periods of time. (Holding sprint/shift, holding forward/W, etc.)
Blacks - Glad I was able to compare these to the reds I've used for the past 6 months. I'd say they require twice as much force to actuate. I still prefer the reds over blacks for my gaming keyboard at home for the aforementioned reasons. For a typist, I would suggest to any prospective mechical keyboard owner to get a tactile switch over the blacks, most likely blues...If you're nerdy enough to wind up on geekhack, chances are you type fast enough to make use of blues. I feel like I would wind up hurting myself on browns from bottoming out too often. Back on topic, though, I don't care for the blacks at all, only because I feel the reds fill any role they may be suited for better.
Clear - I've done no research on these. The clears feel like they are weighted just about the same as the blues, except the tactile feel in the middle is just muddier and less precise than the blues. Do not like.
Ergo clear - These feel like they're also weighted about the same as blues. I'm not sure what the anatomy of this switch is but I could feel feedback almost immediately after applying pressure. These might be nice for the super speedy touch typist. If I was to invest in a 3rd keyboard to be used for mostly composition typing I'd consider this or topre (which I haven't tried before!)
Green - Just feels like a really, really heavy blue switch. I can imagine being fatigued quickly using a full keyboard of greens.
There is my review! Hope it comes in use to at least one prospective buyer, somehow, somewhere. I researched for hours before I finally made my first decision on what kind of switches to get. Will ship out the tester tomorrow, will also post a pic then too!