Changing the keywords in title may change the SERP but it should not have any significant effect for meta tags.
Penguin is the successor of panda that is aimed at low quality and the over optimized sites. There may be something ales after penguin in future.
Just go for the top 10-15 quality bookmarking sites. No need to go for each and every site as most of them will not pay for the time spent.
Do they (link) remain safe after the next penguin updates?
Easy access to the global community is the best part of internet marketing.
You can also look at catalog.webtoolhub.com for more than 20,000 list of web directories.
No change last time. When the next PR update is going to happen. Any idea?
You can either go one way or more than two ways like three ways (but not two ways) as reciprocal links are not favored by Google.
In simple words it should be the number of different pages indexed (stored) in the search engine database.
Now a days only the quality and relevant backlinks counts and also if they usually are in the body part of the articles (in case of blogs).
Meta description tags is what you like to appear in search results and not just the keywords without any readability or meaning. But you can use meta...
I use Google Webmaster Tools and also the Backlink Checker tool from WebToolHub.com
Separate names with a comma.