Yes it is! See this blog post from Peter Saddow:
http://blogs.msdn.com/petersad/archive/2009/08/11/sql-server-on-windows-7.aspx
First, if you have User Access Control in full swing, UAC will generate the following prompt to make sure you're okay with SQL Server making changes to your computer:

If you're not okay with this, obviously, click No, and go about your day as usual. Otherwise, click Yes.
Remember that you need to leave the SQL Server Installation Center running while setup continues. This means you will have two setup icons in your taskbar; in the past, I've attempted to de-clutter my desktop during setup, only to find out that the Installation Center needs to be running or else your temporary files will disappear. I complained about this issue here, but it will not be addressed in this release:
http://connect.microsoft.com/SQL/feedback/ViewFeedback.aspx?FeedbackID=388671
Next, you will get a warning during setup (multiple times; once when you launch setup.exe, once when you select "New SQL Server stand-alone installation...", and possibly through other paths as well) that only SQL Server 2008 SP1 is supported on your operating system:

In the past, this dialog has stopped a lot of people in their tracks, as they thought there was a serious issue and/or that setup would not allow them continue. Rest assured, you can safely ignore this warning, just make sure to install SP1 before you do anything else. While you might already be seeing it through Microsoft Update, you can download SP1 manually here:
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=66ab3dbb-bf3e-4f46-9559-ccc6a4f9dc19
Please make sure you download the right language for your operating system / SQL Server instance. I have seen more than one customer complain that they ran the SP1 installer, but it could not find any components to update, because the language did not match. (The fact that setup couldn't give a more helpful error message is another issue.)
If you are ambitious, you could avoid this warning by slipstreaming your install with SP1 (and optionally, post-SP1 cumulative updates). Peter also has some great blog posts and FAQs on this process:
http://blogs.msdn.com/petersad/archive/2009/02/25/sql-server-2008-creating-a-merged-slisptream-drop.aspx
http://blogs.msdn.com/petersad/archive/2009/04/16/create-a-merged-slipstream-drop-containing-sql-server-2008-server-pack-1-and-a-cumulative-update-cu-based-on-server-pack-1.aspx
http://blogs.msdn.com/petersad/archive/2009/04/24/sql-server-2008-slipstream-frequently-asked-questions.aspx
http://blogs.msdn.com/petersad/archive/2009/06/17/creating-a-merged-slipstreamed-drop-containing-sql-server-2008-rtm-service-pack-1.aspx
Whether you slipstream or not, once setup gets to the point where it is going to launch the Setup Support Rules screen, you may see this error:

This is due to a Windows 7 change in how .NET UI dialogs are closed, and will be addressed both in a future 2008 CU and in 2008 R2 (see Peter's addendum about this issue
here). In the meantime, I have found that the problem goes away if I reboot (as John Paul Cook
pointed out earlier), but not if I simply shut down setup and start over. This likely affects SQL Server 2005 setup as well, since they share the same installation framework; however, if that is the case, I doubt it will be fixed.
John also explains that when you setup SQL Server 2008 initially, leave out Books Online, as a more up to date version is available here:
http://www.microsoft.com/downloads/details.aspx?FamilyId=765433F7-0983-4D7A-B628-0A98145BCB97
Finally, watch this Knowledge Base article, as it is being updated for the final release of both Windows 7 and Windows Server 2008 R2:
http://support.microsoft.com/kb/955725
A side note : can you blue screen Windows 7?
Yes you can! I did this today, using only the SQL Server 2008 installer and Task Manager. Here is how I did this, in a VMWare Fusion virtual machine:
- I launched setup, and got the "Invoke or BeginInvoke..." error from above.
- I quit setup (and an instance of SSMS I had open) and rebooted.
- I launched setup again.
- The Setup Support Rules screen seemed hung, so I opened Task Manager and was surprised to find an instance of SSMS there.
- Being impatient, I highlighted ssms.exe and clicked "Kill Process."
- The dialog I got insinuated that I would lose data. Since I knew I had not opened an instance of SSMS, I shrugged and killed the process anyway.
- I was immediately presented with a BSOD, and VMWare quickly "recovered" by restarting the VM.
This actually hosed my Windows 7 Virtual Machine so badly that I had to delete it from within VMWare Fusion. I would try to start it up, and it sat there frozen. So I deleted it and am rebuilding a Windows Server 2008 R2 VM as I post this (it was released on MSDN/TechNet, and maybe Connect too, earlier today). I should learn to create snapshots before installing software, but quite honestly this is by far the worst outcome I've ever had with a SQL Server install, and the VM was a brand new throw-away anyhow.
SQL Server 2008 R2
Many of the same elements apply for SQL Server 2008 R2. A couple of additional notes, which have been mentioned before but are worth mentioning again:
- You cannot revert to 2008 tools once you install 2008 R2. You can uninstall the 2008 R2 instance, but the client tools will not revert back to the previous version. If you already have SQL Server 2008 client tools installed, you will see this warning on the "Installation Rules" screen in SQL Server 2008 R2 setup:

- You cannot upgrade any existing instance (2008 or otherwise) to R2, because only Enterprise Evaluation is currently being offered, and there is no upgrade path. So, if you already have SQL Server installed, you will need to install a separate instance in order to play. Probably the safest route for now, but since I tried to perform an upgrade, I figured some of you might try it too.
Hope this information is useful.