Hey galileofigaro,
One thing I would recommend that you do would be to check out
Cnet's helpful guide on Mac general maintenance; following these steps can help a slow and sluggish computer.
Is Spotlight indexing while you are trying to work? You can tell by clicking on the Spotlight icon in the top right corner of the taskbar. If you see a progress bar with the indexing of your drive, then wait until that is done, and your performance will improve markedly.
Did you load your data and apps from Migration Assistant or from a previous Time Machine backup? I've heard that this can cause slow-downs in a Mac system, as opposed to copying files over manually. This probably isn't the case, but you never know.
Open all your programs as if you were using your Mac normally. Then launch Activity Monitor: what's the RAM usage look like? If you find that most of your free memory is eaten up, and your system is paging out frequently, then you can always upgrade your RAM. Although 4GB sounds like a lot, heavy programs like Photoshop will soak up as much memory as they can get.
While you are in Activity Monitor, check the list of processes running; is there anything running that shouldn't be, or that you don't recognize? If so, kill them and check back AM frequently, seeing if they come back and restart. Sort your process list by memory usage. Which programs and processes are using the most RAM? In this way, you can get an idea of where your Mac's resources are going.
No one web browser is perfect, which is why I have more than one on my system - if one doesn't work with a particular website, I switch browsers and try again. In this way, I don't have to fuss with browser settings. However, if you are really concerned about Safari's errors, then try clearing out the cache and resetting Safari. Those are usually the top two easiest steps to fix Safari bugs. Ensure that JavaScript is enabled in Safari's Preferences, and that you don't have any pop-up blockers or Flash-kill addons installed which may interfere with graphics displaying on a webpage properly.
I hope these suggestions help you, and that they encourage you to continue to find other methods and solutions. Congratulations on buying your new Mac! Once you resolve these performance issues, I'm sure you'll love it.
