delete me

If you don't have a soup account yet, you can now sign up with Mozilla Persona.
If you already have an account with an associated e-mail address, you can now log in with Mozilla Persona - even if you didn't sign up using Persona.
If you have more than one account registered to the same e-mail address, no such luck: you'll be asked to chose a name for a new account. Welp, at least that one you can log in to with Persona.
If you wish to log in with the same e-mail address into multiple soup accounts, that's no problem: just use address tags. Maybe you know this already, but since the early age of e-mail, it has been a convention to interpret a "+" in your e-mail address - like youraddress+something@gmail.com - in such a way that an e-mail would end up in the correct "youraddress" mailbox, earmarked for "something".
You can use this pecularity with persona and multiple soup accounts (which you should've created as groups anyway, but hey, nobody is complaining): just make sure each one of your existing or new accounts has a different, unique address, such as youraddress+yoursoup@gmail.com, youraddress+yourothersoup@gmail.com etc. This way, the e-mail address is factually the same, and gmail (and maybe other providers) will provide you with a tad more convenience, but practically, it serves us to differentiate between soup accounts.

There are a few parameters that you can add to Soup URLs to filter what content to display:

Filtering by content type
Add ?type= followed by either text, link, quote, image, video, review, event, or file to your Soup's URL to show only posts of this content type.
Example: http://kitchen.soup.io/?type=quote

Filtering by date
Add ?date=YYYY-MM-DD to the URL to show posts on and before that date.
Example: http://kitchen.soup.io/?date=2008-06-01

Filtering by text search
Add ?search=query to the URL to show only posts that contain the text 'query'. Example: http://kitchen.soup.io/?search=blog

Filtering by tag
Add ?tag=tag1,tag2,... to the URL to show only posts that have those tags. Example: http://www.soup.io/everyone/?tags=electronics,programming
To combine these filters, join them together with the & character.
Example: http://kitchen.soup.io/?type=quote&search=blog