I have been a MobileMe customer for a couple of years now. Like KenziK above I let mine auto-renew. I'm not terribly worried about the transition as my renewal date is late October, very close to the iCloud deployment date, so I'll get my full year's sub worth of usage, plus the free time for transition.
I am a little bit concerned about the aggressiveness of the strategy, although maybe I shouldn't be surprised this being Apple. Whilst core components are being transitioned across (Mail, Calendar, Gallery etc.) there are worries about retaining data (they never did very well moving the online Calendar over to the newer system).
Also, iCloud has 5Gb data allowance. A MobileMe sub has 20Gb. As a goodwill gesture, all existing MobileMe subscribers should at least get the same data storage capacity to enable a smoother transition.
Finally, are some of the other features of MobileMe going to have an analogous component in iCloud? iDisk is already a point of concern. What about the Gallery features such as e-mail upload? This, along with the iPhoto sync, was incredibly useful when I got married recently. We put the album web address and the e-mail upload address on the back of our wedding programmes and have so far collected almost 1000 photos, which all auto-download into my iPhoto and sort into time/date order automatically. Will things like this be available under iCloud?
And finally (seriously this time) - the e-mail that came out last night (or yesterday afternoon if you're stateside) stated again that iCloud is for iOS5 and OS X Lion customers only. Lion excludes all Macs with processors older than Core 2 Duo. iOS5 excludes the first 2 generations of iPhone. I am sure there will be a percentage of MobileMe customers who are therefore ineligible for iCloud but for whatever reason may not be able (or want) to upgrade in the time window (e.g. financial etc.). What happens to those poor sods? For those who find MobileMe very useful (like myself) but are using older hardware (I'm not in that group thankfully), it forces an upgrade.
I can't decide whether to say "Well played Apple. Well played." or make a point that Apple's increased userbase means they have to be more careful about these forced transitions and obsolesences. This one is particularly nasty if you fall outside of Apple's designated favoured group.