I have been using Plus Addressing and Gmail filtering for some time now. It’s remarkably useful as I can set up filters for my incoming emails on their “to” address. Filters on subjects or “from” address do not work well sometimes. I assign ‘firstname.lastname@example.org‘ to each website I register, then use filters to apply the website name as label. Labels in Gmail are similar to folders, but they are more like categories or tags.
Back in July 2006, I wrote a tiny Ruby On Rails app “mail2rss” at work, inspired by mail2rss.org, to cut down emails sent to the team from various applications we manage. It uses procmail to pipe all emails sent to @example.com to ActionMailer to store them. For example, an email sent to ‘email@example.com‘ is saved in a mailbox “app1” and tagged with “tag1”. Actually you can use more than one +tag, e.g. ‘firstname.lastname@example.org‘. The mail2rss is one of my favourite tools.
Try Paul Warren’s RFC822 email address validator.
BTW, NYTimes.com registration does not allow plus-addressing.