Being rolled out with only a day or so to spare before Nokia World hits is a 'service pack' for Symbian Anna, claimed to bring performance and usability benefits, plus faster email and messaging, quicker GPS fixes and a mysterious 'more' (presumably including minor bug fixes). So far we've only seen this (today) for our Nokia N8s, though I'd expect other Anna devices to also get offered this fairly soon. What's not to like?
The update is a mere Megabyte and is offered both over the air (look in 'Sw_update' in Applications) and via Nokia Suite. As you might expect, your phone will restart during the update. Note that the service pack doesn't change the underlying firmware version (v25.007, typically), i.e. it's an 'application level' update, not something that patches the firmware.
Email does in fact seems snappier after the update, although the enforced restart always helps too....!
Recommended as and when your device gets offered this.