I ran my N9 for 9 days, 4 hours and some number of minutes (information courtesy of the Battery Usage app). From time to time there was some lag, particularly starting applications. A lot of email (3 accounts), multiple calendar sync (with CalDAV), SMS, RSS and Facebook feeds to the notification screen, maps, web browsing, music (using FLAC as the encoding format), video (mostly downloaded using CuteTube), the above mentioned Battery Usage app running all the time, oh yeah - and some phone calls. WiFi, Bluetooth on always. Usually a half dozen apps running all the time (clock, calendar, battery usage among others). Finally it seemed like it just got gummed up (how's that for a technical term?) so I shut it down and restarted (probably only the third restart in the time I've had it.) Smooth as glass again. As yet I haven't turned Developer Mode on. I'm not in the habit of rebooting my phone often - I used to let the N900 run for a l-o-n-g time. Anyone else seen anything like this?