Don't worry for manual or auto submission. I suggest do it semi automatically. It will help you in making your job easier for manual submissions. Try socialmarker.com and socialsubmitter.com, check them in google if URL is wrong.
Tool is not perfect if you need quality bookmarking then you need to do it manually, remember only Social bookmarking is not enough, you need to do it properly and manual is only perfection
I am using bookmarkwiz, which doesn't have to many bookmarking services available but it is really reliable compared to for example Bookmarking Demon.
Problem with a lot of the automation tools is they are either expensive like SEnuke or they don't work on major sites such as Digg with BMD. Manual is very tedius but if you do it for say 1-10 of your core important pages manually, then perhaps the others automatic you will get great results.
I've tried using bookmarking demon but for some reasons, it is not working. Perhaps, there is something wrong in what I'm doing.
i think you can use ping.fm for auto posting. I would like to strongly recommend you that you bookmark as manually.
Social Bookmarking Service should be done manually. Many websites demand space separated tags. many demand comma separated tags so according to that you can submit only when you do it manually. So friends go for manual and if you have scarcity than you should hire someone who can provide you quality service at affordable price.