The Postal Service is not making a big deal about its latest rate increase, in part because most postal customers won't notice the difference, until they buy new stamps.
About six months ago, all first class stamps became 'Forever' stamps, so even if you bought months ago, they're good, even with the rate increase. But, if you're using stamps that say 44 cents, Natalie Dolan, with the Postal Service, says you can buy the one cent additional stamp to bring it to the new first class rate, 45 cents.
Dolan also says not to worry, about recently mailed items with the old rate on them--they'll be lenient as the systems catch up, so don't expect returned mail for postage due.
Besides first class, other rates also went up: post cards, which were 29 cents, are now up to 32, and there are increases for priority services at well. The Postal Service website has details, as well as discounts if you do your mailing online.