Facts we should all be aware of direct from http://blog.kissmetrics.com/:

Twitter:
Tweet for retweets around 5pm;
average CTR – between 1-4 times per hour;
highest CTR at midweek & weekends between noon-6pm

Facebook:
Shares peak on Saturday, Noon sharing once every 2 days.

Email campaigns by hour: (important to segment campaigns by Timezone)
6-10am – Mails on the topics of Clothes, Live events, Restaurant & consumer goods.
10-Noon – Do not Disturb
Noon-2pm – lunch break (news / magazines mails)
2-3pm – in the zone (working)
3-5pm – Property & financial services emails
5-7pm – Holiday promotions / B2B promotions
7-10pm – Consumer Promotions (clothing, sports / gym etc)
10pm-6am – sleep.

Bounce Rates, Open Rates. Click Rates & Abuse Reports – are highest at weekends and early mornings
(abuse reports are mails that constitutes as ‘spam’)

Click Through Rates (CTR) & Unsubscribe Frequency – Highest at less than 4 per month… but frequency is consistent over 4.
Highest Unsubscribe rate are for subs less than 10 days old.
CTR of Subs: highest in under 10 days… also spikes around 4months

Blogging:
Pros for High activity times: More Visitors / comments
Pros for Low Activity times: Less noise & easier Front pages promotion.
Posts are read in the morning
Blog views highest on Mondays at 11am.
Best day of the week for comments – Saturday
Best comment hour: 9am
Increase posting frequency to increase unique views.

Takeaway:
Frequency of emails campaigns, posts, tweets works! More than once per day, is OK. Evenings, Weekends and early mornings is the ‘golden time’. The 9-5 is when people are working.

Personally I hold back on multiple posting due to annoying friends, however the effect on finding new business, outweighs that annoyance to friends, who probably do not ever buy from you anyway.