It really is aimed at the slightly more tech inclined than, say, a typical iPhone user. You cirtainly don't have to be a genius to use it. In fact, I think the interface is more intuitive than an iPhone. But it gives you a lot of power. Like you can multi-task, and have as many crazy apps open as you like. Of course that means that it will slow down, but as long as you realise that having loads of apps open is going to slow it down, you will be fine. Same with loads of widgets, etc. If you like linux, and hacking, then this phone offers hacking capabilities that no other phone comes anywhere near to. But you don't have to do that.
Nokia have been a bit callas with it however. Like it doesn't work with their Ovi store, and getting it to work with the old PC suite is tricky, and there are only a few functions that work. Lack of OOTB MMS support was pretty stupid as well. Luckily most of these problems have been solved by the community, but you need to know where to look. Most reviewers wont bother to go exploring maemo.org to realise the phones potential.