In regards to marketing your sites, we all know that directory submissions can aid your SERPS however how much if at all does this affect our page rank? Any ideas?
Directory submissions will improve your rank. By how much - it depends if we are talking about free directories or high quality paid dir. The quantity makes a difference too.
I personally think that Pagerank is just a title made by google which really doesnt have much value unless your selling a site. I have seen sites with great content that have been around for a while that have high rankings in the SERPs but have very little PR. I mean does it really matter if you get great traffic but your Pagerank is low. Not really unless your a directory or some other site that depends on that kind of an image.
What is important is the quality of the directory... Does it keep the listed sites tightly on topic? Are the listings free from spammy keyword stuffed titles and descriptions? How many pages long are the categories? How many listings to a page? Does only the homepage have PR? (Then it is most likely a poor investment of your time.) Those are just a few quick things. Quality is what is important; not price.
Definitely DMOZ submission increase the page rank since it is inherited by many sites. Some other directories which are very popular is also helpful.
Nobody can answer because it varies a lot. Though overall it gives +ve kudos in pagerank but 'real' value of pagerank juice depends on PR of the page on which your link is placed. Its better to submit in few paid directories than dozens of free directories {which hold no PR for deeper pages on which your link is placed}
Any directory that has PR on only the first page is a directory that has most likely been set up on an expired domain. While the vast majority of these folks are hoping to making a quick buck - hence the monniker QBC (quick buck crew) - there are a few here and there that intend to use the existing PR to get a quick start. Personally, if a directory only has PR on the homepage, I don't submit - I don't care if it is a free or a paid directory. There are many free directories that are well maintained and DO HAVE PR on internal pages. I know this for a fact! I own one. Likewise, there are many paid directories that are not well maintained and DO NOT HAVE PR on internal pages. Evaluating a directory simply on whether or not it is free or paid is like evaluating the usefulness and quality of a piece of software simply on price. There are amazing free programs available just as there are many overpriced programs on the market. I use IrfanView almost daily and wouldn't give it up without a fight as it does some things easier and quicker than my much more expensive copy of PhotoShop.