This has changed a little with 10.7 and you'll want to note that this uses IPv6 almost entirely so test with ping6 and traceroute6 to debug things.
It's no longer done via @computername.mobilemename.members.mac.com, it's now done via members.btmm.icloud.com, and its no longer as simple as your mobilemename.
Step 1: Find out your iCloud BTMM domain
Either of these commands will provide your BTMM domain:
# dns-sd -E
# mDNS -E
The output is formatted slightly differently, but what you're after is the numeric ID, it'll be something like 12345678.members.btmm.icloud.com.
Step 2: List Computers
You can use these tools to browse that domain for services, e.g. for ssh servers:
# dns-sd -B _ssh 12345678.members.btmm.icloud.com
Or if you already know the hostname just access it directly as computer-name.12345678.members.btmm.icloud.com. (Any spaces in your computer name will be hyphens in this domain).
You can only access this from a computer that is also set up for BTMM on the same account, because this hostname will resolve to an IPv6 address that is really the end of an encrypted network tunnel between your BTMM computers.
If you want to see the IPv6 address for a specific host, you can type
# dns-sd -G v6 computer-name.12345678.members.btmm.icloud.com
And it'll output something like:
17:37:47.504 Add 2 0 computer-name.12345678.members.btmm.icloud.com. FD11:993E:64AE:4DEA:011F:FBD1:F444:11A1%<0> 152
Step 3: Connect
# ssh username@computer-name.12345678.members.btmm.icloud.com
Note
I'm not sure if that number will ever change, so you may or may not need to repeat Step 1 at some point later on...
You actually can set a rule to move the received message to different folders according to the sender, either your friends or your university's teach.
In terms of the automatically sending message to different receipt with different account, I can't figure it out, but there is a manual way. In the mail.app Accounts setting, leave the "User only this server" un-selected. So that, when you compose a message, there will be a SMTP server selection drop down list allow you to manually select which SMTP server you are going to use.
Best Answer
The short answer is you get to keep MobileMe as it is until June 30, 2012.
Sometime between when iCloud launches (tomorrow?) and next June, you can choose to learn about and use iCloud (assuming it meets all your current and future needs) or find another email provider.
It is clear that Apple has said you will lose access to you me.com account if you don't move to iCloud by then so unless that changes, you should plan some action.
If things go as planned, we will all get a public look at things this week. Perhaps read some official documentation in the next month you. The future is unclear today before iCloud has launched, but you have 9+ months to worry about this...