Apart from Dmoz and Yahoo which are the most valubale directories to get a listing, which really helps is attaining SERPs...?
There are many to select from ranging from PR5 Up, and many new quality directories that have not yet been Page Ranked but still offer affordable submissions Take a look at these lists most of the Directory sites posted on DP in the last year will be on these lists Here are a large selection to choose from with many Directories to select from http://forums.digitalpoint.com/showthread.php?t=150381&page=6 And here is a list that someone added on DP recently for 2007 http://forums.digitalpoint.com/showthread.php?t=207790&highlight=NLRMedia
Make a search on DP . This has been asked before aswell.. btw http://www.directorycritic.com/free-directory-list.html http://info.vilesilencer.com/ Make a search on DP ..
Id say there are some key general directories and sites to get listed in such as Alive, Aviva etc. in addition getting listed on a relevant niche directory will do wonders for your SERPs.
Which are the most valuabe directories to get listed? -Related niche directories is the most valuable.
Here is researched list of sites that will be very beneficial to be listed in this year: http://www.blueraccoon.org/blog/directory-hotlist-for-2007/
Is there an article on strategies for posting on Directories? I heard that it's not so good to use the same description and copy across all directories. Is this true?
Hmmm i think every 10 is a little over the top - what you need to remember is that although you maybe submitting (say for example) 100 submissions in one go, this doesnt mean they are going to appear immediately. Approval may take anywhere from a couple of days to a couple of months depending on the directory and you never know when that site with your link on is going to get indexed! Also look at different link titles for your site(s)...
Getting listed in niche directories won't necessarily be better for your search engine position, but it's more likely to bring you relevant traffic through the directory itself.
The best directory to get listed in is all that have the category you are targetting in the SERPS themselves. I did only a small nubmer of submissions (around 200) about a month ago, and a quick look at the SERPS has put me onto page 1 for an additional 10 keywords I was targetting. The only thing I did was to submit to directories.