I think a lot of the complaints are not from N900. People usually like their N900s, but they do fear for its future and whether they would end up with an obsolete device in a year's time. The main reason for this is Nokia's attitude. IMHO, following are the main reasons why people are complaining and many of them are legitimate:

1. When they bought N900, they thought they were buying into a platform which would form the basis of Nokia's smartphone entry. However, then came Meego and the news that N900 won't be officially supported
2. A lot of people (that includes me btw) were hoping that with the N900, Nokia would hopefully finally get the new dynamics in the post iPhone world that it is not about hardware anymore. With Apple supporting its two year old phones in the new firmware upgrade, I think people find Nokia's contrasting attitude very disappointing. Personally, I think Nokia shot themselves in the foot here by treating their most loyal customers shabbily. I have been leading NPD for the last 10 years and there is anything I have learned is to keep your core customers. Nokia should probably go and study about NPS (Net promoter score) and network effects
3. Last and probably the biggest reason is Nokia's selective open source adoption. Nokia adopted open source when it suited them i.e. getting a lot of pre built software and application echo system without having to do the work themselves. However, they left the other half out about open communications and transparent roadmaps. Again, as anyone who has studied economics and Nash equilibrium would tell you that open roadmaps are actually great for both customer retention and also to make sure your competitors don't enter your markets. That is one of the reason Apple announced the features of their next OS as many of the Apple loyalists had started cribbing about lack of multitasking etc. Nokia however are all about keeping mum. There are genuine reasons for that as that gives you more flexibility, but in this case that is causing more harm than good

So yes, IMHO Nokia have actually screwed many things up with N900. As I said, having headed product development in associated industries, I can see too many holes in the process to say Nokia is blame free here. But I am not worried because Nokia will actually have to pay for it in the medium term. Justifying actions to users never works retrospectively. You have to manage their expectations from the very beginning, which is what wasn't done in this case.