The screen on the N900 is very wide (800 x 480). This obviously allows the browser to show webpages as they were designed to be shown. It's not long ago when everyone was still designing their sites for 800 x 600. Herein lies a problem: Any webpage that is 800 pixels wide and fully zoomed out, has text that is too small to read on the N900. So, of course we zoom in. But if the site has columns that are wide enough to cover almost the entire 800 pixels, we have to start scrolling sideways the minute we start to zoom in. So it's a choice between sideways scrolling or text that is too small to read.
The iPhone has a portrait-mode screen, so if the site uses a relative layout, making the text column for instance 80% of the browser width, the columns still won't be very wide. The HTC Hero reflows all textareas so that sideways scrolling is (almost) never required. The N900 does neither and I ended up sideways scrolling on quite a lot of pages.
The best solution, it would seem, is to choose a larger font. You can change this from the "easily" accessible Menu -> options -> adjust view -> text size -> Large. This won't make the columns wider, so the text can be made big enough to read without side scrolling.
Another solution would be to
Another irritating thing, that will probably be fixed in the future is the issue of kerning. Take a look at this screenshot: