Shutterstock:
Likes - Sales, great help on forum, unpoliced forum, fast reviews
Hates - Not terribly happy with the reviews but its a two way street when it comes to getting photos accepted

iStock:
Likes - Sales are as good as SS on half the portfolio, statistics are great, great feedback on rejected photos
Hates - Disambiguation isn't the greatest, could use a better uploading tool

Dreamstime:
Likes - Upload process
Hates - Narrow range of images accepted, ridiculous rejections, some outrageous rules and changes to the site

Fotolia:
Likes - Decent sales, most EL sales of any site
Hates - Nasty uploading process

Stockexpert:
Likes - Easy uploading, thats about it
Hates - I find the rejections quite inconsistent (for me) since they accept some and reject similar images as stuff they aren't looking for. Sales aren't great. Someone should tell reviewers that "We aren't looking for this type of image" is not a generic rejection

LuckyOliver:
I need $25 to a payout. Its taking forever and I'm kind of getting impatient.

BigStockPhoto:
At max $10 a month in a good month, there's not much here to talk about but I think its a decent site and the low payout is really good.

Featurepics:
No sales, stopped submitting a while back.

123RF:
Will be uploading more since all I have to do is upload through FTP.

Crestock:
Have never actually been to the site

Alamy:
Will be preparing an Alamy submission very very soon. Prospect of RM is much more exciting.