As mentioned grinders are excellent "if" you know how to use them properly. It also depends what you're cutting and how quick you are bluntening/wrecking chains. If I'm wearing chains out in 10 minutes on filthy, old, dead, termite infested hardwood (it happens!) then I tend to swap chains out and grind when I get home. However if you only need to sharpen 3 or 4 times a day then by all means whip out a file - I have been lately because when I get home I can't be stuffed grinding chains. I do tend to grind my chains after about 10 filings. They're not too bad but do get the odd inconsistent cutter lengths. Angles always seem to be OK.
In saying that, and I've mentioned it numerous times before, some people just can't file properly despite thinking they can and as always in life some people can't be taught (people like this exist, I've worked with them
) or don't want to learn. I have a mate who is very handy and quick to work things out but has bought a grinder because he can't file very well, does a lot of firewood cutting, and with two young kids who are a handful he'd rather not spend hours learning to file. At least with a grinder you can go cutting wood and know you'll get adequate to excellent results. Many people who file are likely to get a surprise if they threw their chains on a (quality!) grinder as they suddenly realise that their angles and cutter lengths aren't as good as they thought they were!
Sadly most of the guys who bring their chains to me have only brought them to get a replacement as their chain "don't cut no good no more". Generally it is a good chain just sharpened badly. A quick grind to retrue it and set the depth guages and after they've used it they think it's christmas. Remember that the vast chainsaw using population see a chainsaw as a tool and nothing more. They don't have the same love affairs with their saws/chains/cutting that many of us on AS have!
Once again, not bagging filing, just making people aware that proper filing isn't as easy as some people make it out to be. Some people would rather grind and swap chains if they have to and as has happened numerous times on this site shouldn't be burnt at the stake for doing so.
Remember: Just filing a chain so that it cuts better than before does not constitute good filing and poor filing is rarely as obvious on shorter bars (ie: less than 32")