Had the SD-90 for about a week and overall I'm impressed with it.
First off, the video quality is very good. Played videos back on a 37" HD TV via HDMI link direct to camcorder and the videos are crisp and clear (set at the default recording quality, which I think is the second highest its capable of). Maybe some slight blurring when panning very fast and colours could be at times more vivid, but there are a multitude of scene and manual setting I have fully explored yet. Generally, pictures look great. Camera works well in relatively low-light (tried inside under electric lights) and the auto focus is very quick.
Sound quality is OK via the twin microphones at the front of the camera. Seems to cope with ambient and near sounds well (not tried on a windy day so can't comment on noise pickup). Tested the range of the camera at picking speech, wasn't great, I'd estimate it was OK once within around 10 metres. Obviously sound issues could be addessed using the convinent mic port on the side of the camera and a directional mic on the shoe on the top of the camera.
Controls are simple and well placed. The touch screen works well, although using the menu to the side of teh screen (when video is displayed) can be a tiny bit fiddly. As with all touch screens the chunkier your fingers the tricker it will be. The camera is pretty feature packed. Detect faces in almost all cases, and you can have it recognise up to six faces (which you can set as a prioirty for focus, e.g. set the bride and groom as the priority focus at a wedding). The recognitions weren't 100% but was acceptable.
Build quality is very good. The camera settles neatly into your hand. The zoom is outstanding, the clarity of detail of extreme distance objects blew me away. However, with such a small camera (with no shoulder support) a tripod (dirt cheap on ebay) is a must.
Battery life is not the SD-90's strong point. With the standard battery you get about an hour playing with it and using all the different features. The camera can be charged off the mains while still in use, but this isn't always ideal. Spare batteries and fairly pricey and not yet widely available. I intend to try using something like the Peeble (Veho VCC-A008-PBP-XT Pebble Portable 5000mAH Battery Pack Charger for iPad/iPhone/iPod/Smartphones/PSP/NDS/NDSi/GPS
) but haven't got round to checking it has the correct adapter.
Memory is less than issue. The videos take up a heck of a lot space, but SD cards can be swapped in and out quickly and easily. 16 GB gets you about 2 and a half hours at high quality, which will set ou back £20-£30 per card. The Panasonic software is better than expected but still not amazing. Films in AVCHD format, which is decteded by Microsoft media player/movie maker by default. I'm sure there are convertors to mroe firendly formats (and it may be possible in the Panasonic software). If I find a solution I'll try to add it to this review.
Overall I give the SD-90 five stars. Basically it does the job I want very well, with several features I jhadn't expected. Of course its not a pro camcorder, and the battery life is an issue (as it probably is for many camcorders - if you want extended battery life you'd best check spares/mobile charger options before buying any camcorder). However, if your intended usage is along the lines of filming the kids at Christmas, a family wedding or a day at the seaside, then you will find the SD-90 extremely capable.