Vista, SP1 installed or not, does not offer the freedom of movement that users are looking for. After my installation of SP1, it was almost immediately uninstalled. I gave SP1 a fair shot, but it was not worth the plague that it cast upon my notebook.
Reason 1: Driver Issues
After the installation of SP1, my sound driver stopped working. Yes, I should have done a little more research before my installation of SP1, but seriously... Its supposed to be an update for compatibility. The last thing you expect with an update that you're told, directly from the developers I might add, that it's going to enable you to have more hardware and software work with your machine is for hardware/software to stop working. Its a known issue that there are driver problems with RealTek audio drivers and even a driver problem with chipsets that were thrown into thousands of PCs and notebooks that are "Vista Capable". The chipset in question is Intel's 945G Express series. There is a driver update to solve the problem, but make sure you update the drivers for every piece of hardware you have before installing the service pack. Sure, for a techie thats simple, but the average user doesn't even know what a driver does, let alone know where to look for or install them. RealTek, nor Microsoft, has not released a driver fix for their problem, but after installing SP1 if you go to Control Panel -> Sound, it will open a pop-up that will prompt you to "Fix" the driver problem. It has worked for me for my headset and notebook.
Reason 2: Random Freezes
Before I installed SP1, my Sony VAIO VGN-NR110E ran remotely fine. There are problems with Vista load times here and there, but thats expected with a gig of RAM, which the OS uses 65% plus of. However, I did not have a problem with the notebook freezing up on me. About an hour into SP1, my laptop froze up on me. Another reason why SP1 only saw a little over 24 hours on my notebook.
Reason 3: Does not fix what most users were expecting
With SP1, Vista will still be the memory hogging selfish little OS you saw before the service pack. You will most likely not see "more compatibility" as promised, and I hope you are not hoping it will be the ultimate fix to that little problem that you can't find an answer for. My little problem is with Microsoft's Network Client (As its labeled under software that handles my connection.). After Vista is completely booted, I right click the network icon in the taskbar. Nothing happens. I wait, and right click it again. Nothing happens. I give it one more shot, and I finally get a menu. Yay! Oh wait... I can't select an item from the menu. Hovering over an item in the menu does not trigger the "hover effect" that shows the item you'll select if you click. I can let it sit there all day and it will not trigger the effect. I click anyway. Nothing happens. Menu will not disappear even after clicking off of the menu. Right clicking the icon again does nothing. It will sit down there on top of every window I have open.
10 minutes later it may be gone, it may not be, but eventually I will be able to select an item from the menu. Finally! Oh wait, I click "Connect to a network" and nothing happens. I click the item again, and a window appears. Finally... Oh... Never mind. The window appears blank, and sits for literally 10 minutes before it will show a list of networks. Being on a notebook and using multiple WiFi connections at my campus, I need to be able to switch networks quickly and efficiently. I would try to connect to it via the network menu under control panel, but that takes equally as long to load and does not offer a "New connection" option. For the record, the notebook is running Vista Home Premium. For the listed wireless connection, it does not include an option to connect and scan to a wireless network. The only real connection I can make is for someone to connect to my notebook via VPN. That won't do me much good.
I would contact Microsoft support directly, but they want to suck $59 out of my bank account for contact via phone, email, or live chat. No thank you. I would like free support for software that I'm forcefully stuck with, and hardware that will not allow me to downgrade to XP because a lack of driver support. If not free, at least drop the price so that users can actually afford to have their problems fixed.
In conclusion, don't download SP1. If you do, just be sure to update every driver on your machine and pray to the Microsoft gods that the service pack will run smoothly.