Hey grp_photo. I think you already know as much as I do about all this... but here's my tips.
If you plan to submit to Fotolia, place the 7 most important keywords first. You can rearrange them after upload, but it is a pain.
Make sure you place a comma between keywords. For some dumb geriatric reason I keyworded a whole batch in PS without commas and of course only the first three words appeared upon submission. Oddly, they all arrived on IS though - the most difficult site.
I don't know if you want to do this - but I just went through all my photos at one site and placed my user name in the keywords. This makes it easier to find my photos in a search on their affiliate sites. (LOL, also, everyone who has stolen your keywords and has been too lazy to review them pop up when you search your user name.)
Some people here swear by prostockmaster or cushy stock - I don't know - never tried - but I think they have keywording tools built into them.