It is entirely possible to have lots of applications opened at once and switch between them. You can use a hardware button to open the application switcher or tap its on-screen icon if that is visible, then switch to a new app or close any you don't need any more. Apps can be slow to load first time round, but thereafter they switch quickly. Importantly, there is a lock button which disables the touch screen and hardware buttons.
There is 2MB of built-in storage and an SD card slot for adding more, and the N810 Internet Tablet supports SDHC. You can connect it to your PC using the supplied cable, but sadly Nokia has made its connector microUSB rather than miniUSB so the chances are that the generic cable you already carry around will be no good for this job.
The Linux-based software is generally quite impressive. It looks neat and for the most part runs smoothly. There is a fairly active developer community, and the 122 downloads that were listed as I wrote this review includes games, multimedia, Internet apps and more. However, don't expect as many add-ons in comparison to other handhelds formats such as S60 smartphones or Windows Mobile.
In the end the N810 is a really frustrating device. I rather liked using it, and if somebody presented me with one I'd say ‘thanks', and keep it in the front room for a bit of entertainment while watching telly. But with a relatively small add-on software base and no SIM I just don't see the N810 carving out much of a niche for itself. Which is a pity.