It seems we have a monthly trend of service maintenance kicking into effect with Nintendo online functionality, as more "Emergency Maintenance" is on the way in major territories next week. There was a round of downtime on various platforms on 28th January, and a similar period is on the way from 26th February, or very late on the 25th if you're on Pacific Time in North America.
The broad range of affected services, including DS games, suggests that we shouldn't expect any visible changes on our systems or online games. It seems this is becoming a regular process for Nintendo, though the UK message sensibly calls it "Temporary Maintenance", as opposed to Nintendo of America's rather excitable word choice of "emergency". In any case, below are the U.S Pacific times and details, accompanied by the matching UK times in brackets — the maintenance is at the same equivalent time in each region.
From Monday, February 25, 2013 11:00 PM - Tuesday, February 26, 2013 5:00 PM Pacific Time
(From (approx.) Tuesday, 26 February 2013 07:00 to Wednesday, 27 February 2013 01:00 UK time.)
Pokémon Black Version
Pokémon White Version
Pokémon Black Version 2
Pokémon White Version 2
From Monday, February 25, 2013 4:00 PM - Monday, February 25, 2013 5:00 PM Pacific Time
(From (approx.) Tuesday, 26 February 2013 00:00 to Tuesday, 26 February 2013 01:00 UK time.)
Match Making, Ranking, etc.
NINJA GAIDEN™ 3: Razor’s Edge
WARRIORS OROCHI® 3 Hyper
*During the emergency maintenance, parts of the affected services may be intermittently unavailable.
So there you go, just so you don't wonder what the heck is going on (particularly with Pokémon services being down for the longest period), and at least 3DS seems to be dodging the bullet this time around.