The following announcement on dreamstime website:

May 13, 2009 (09:48)
Contributors: Upload limit is now increased from 100 to 150

Below is from FAQ.

Why are you restricting the number of uploads to my account?
In order to manage the number and quality of images that are submitted to the Approval Queue, we have to place some restrictions on uploading. These have been revised as of May 2009.

If you are uploading good quality images, that are marketable, you will have no limits generally. But if you upload a lot of images and delete them (this wastes bandwidth and server space) or you submit a lot of images that are low quality or not very marketable, you will have some restrictions, which will be removed if you take the time to learn what is going wrong with some of your images and how to improve your shots.

These are the current upload retrictions that you might run into, updated May 2009:

New users with less than 15 total approved images are limited to 15 images in the Admin Approval Queue at a time
Users with an approval percentage of 50% or less are limited to 10 images in the Approval Queue at a time
Users with an approval percentage of 70% or less are limited to 20 images in the Approval Queue at a time
Users with an approval percentage of 85% or less are limited to 40 images in the Approval Queue at a time
Users with an approval percentage of 92% or less are limited to 50 images in the Approval Queue at a time
Users with higher than 92% approval percentage have no limit.

Images that are uploaded and deleted will also lower your rating. Deleted images count the same as declined images.
An approval rating of 50% means that half of your images were approved, and the other half were deleted by you or denied. A rating of 95% means one out of twenty images is not approved. So it's a ratio of approved images compared to all images that were approved, deleted or denied.

Remember, uploading images and deleting them affects your rating too, so please take some care not to upload images you don't intend to submit. Thanks again.

I got accepted at Istock a little over 2 months ago.  It took me two or three tries; I can�t remember, I must be getting old.

About 2 weeks ago my 15 year old daughter got accepted.  On her first try she got the "Images are very similar in subject matter or style" rejection.  On her second try, 2 of 3 were accepted and on her third try her last image was accepted.

Her first images were accepted and online a few days ago.  She had her first sale yesterday so she was pretty happy.

In answer to the OP question, I think it is worth it.  IStock is my number 2 earner. I am only two months into this and my portfolio is small (91 images) so who knows what the future holds.

I had three isolated objects accepted in my submission.  I had heard that you should have a diverse group of images, which is what I tried to do.  I later read that some one submitted 10 isolated images and got approved.  I also saw some one with 10 bird pics that got approved.

Here is some data from a newbie.  I started contributing to microstock sites in mid-January.  March was the first full month in which I had images on SS and IS.  My portfolios range in size from 52 on IS to 149 on StockXpert. Not suprisingly March was my BME on all sites.

SS     56.78%
DT     11.49%
IS        9.69%
FT       8.42%
StockXpert     4.98%
BigStock     4.86%
123RF  3.79%

Done.

http://www.stockxpert.com/browse_image/view/35630631

also, when Fotolia rejects an image , they give very specific reasons, you know when you correct that reason your next uploads will be accepted.

Fotolia does not always give very specific reasons for rejections, look at this one:

The image contains one or more technical problems:

Blurry or out of focus
Over/Under exposure
Framing problem
Over or under saturated colors
Problems with contrast
Noise or Pixelation
Quality of routing
Interpolation problem

Done

http://www.stockxpert.com/browse_image/view/34433021

I've been having problems getting the fotolia.com page to load using Internet Explorer for about a week.  Both at home and at work.  Using Firefox it worked fine.  This morning IE workeed.

If one takes a picture of say a cell phone and removes the logos, can the image be used for microstock since some one with knowledge of cell phones could easily identify the phone as a model XYZ made by company ABC?

In the forum Fotolia Q&A � Frequently Asked Questions (dated 29/03/2008) it states the following:

Q. Can I edit keywords after the image has been accepted?
A. No.  You need to get the keywords correct when uploading and in the correct order.  Put your most relevant keywords first.  They cannot be reordered or changed.

Q. Keywords and Phrases
A. Always put the most relevant keywords first.  Do not use phrases as these cannot currently be found.  Use single words with commas between. 
For instance for the bird called a "Tree Creeper" do not use:  tree creeper, but do use:  tree, creeper,  Even though this makes the keywords look incorrect as there may not be a tree visible it is part of the bird's common name.

Does any know for sure if the keyword order is truly important?

Some site allow phrases, are phrases important on these other sites?

I guess my question really is, how do you deal with the various keywording rules across all the sites you submit to?

Thanks for all the advice everyone.  I have a lot to mull over.

I definitely won't be quiting my day job.  This will hopefully be a way to have some fun, learn more about photography, and earn a little extra money.