I realize that SEs don't use the kw meta tag much anymore, but I still want them to look right (just in case).
Which keywords should actually go in your keyword meta tag? Should you only include those you are optimizing on that page? Or should you include all possible keywords found in the content on that page?
For instance, you may be targeting "red widgets" on a page, but you also have words like "widget store" and "widget specialist" found in the content on that page. But if those additional keywords are not part of your optimization strategy for that page, do you still include them in the kw meta tag?
The list should be short. Remember that every single character means that your file is one bit larger and that a search engine sees the "real" content one bit later. Yes I know that these are small disadvantages, but it all adds up.
I suggest that you let the list contain those keywords that you have optimised the page for. And then perhaps a few more that are on the page and where you consider the page to have some degree of "supportive" function for those pages that are optimised for those keywords.
Yes, I agree that the kw tag should be short. What about words in the content that should be pretty obvious to the search engines, such as your company name and location? Would you leave them out of your kw tag?
You may want to include the location in your tags and in your optimization as well. You can achieve high ranking with keywords+location. Depending on your product and location, the KEI may be suprising.