I'm pretty new at this advocate thing, but thought I'd throw my thoughts out there on how TF2 is running for me under Linux. I've posted my computer's vitals at the bottom of this post for those that are interested.
Installation
The installation was (relatively) painless. Not nearly as simple as installing a native Linux app or installing a Windows app under Windows, but much easier than installing a Windows app using WINE. I did get bitten by the Another Instance of steam is already running during updating of steam problem when trying to load Steam (so I could load TF2 naturally). I followed Jeremy Newman's tip at the end of that thread, but it did not help me. I tried killing Crossover and restarting Steam, rebooting and just starting/restarting Steam over & over. Eventually I got past the error, after a couple dozen tries. Once I got past the error, Steam has been running very smoothly. TF2 installed just fine and it even downloaded quicker than under Windows. :)
Playtime
Double-clicking on TF2 in Steam doesn't always launch the game. Sometimes it will act like it's starting and then.... nothing. Sometimes it launches just fine, not sure what's going on there. Right-clicking on TF2 and selecting "Launch game..." starts TF2 everytime with no problem. TF2 opens up just fine, the menu fonts are a bit wonky but still readable. Though the fonts in the server list are only just barely readable. Select a server, double-click it and TF2 starts connecting. This seems to take a long time, but then again it feels about the same as connecting to a server when running TF2 under Windows XP. Once I get connected to a server, all the pre-game menus seem to work just fine. Once I select a character and get to playing, I can distinctly feel the game is running much slower. It feels like I've got really a bad ping-rate to the server (300-500) even though the game reports my ping-rate as less than 100. Still it's not entirely unplayable. That is it's not unplayable for most classes but trying to play a sniper is an exercise in futility. Using the sniper's zoom, makes the game unplayable. When zoomed in it takes seconds to move a single step (forward, side-to-side, or backwards); making it impossible to snipe even a heavy weapons guy. Hopefully, the next release of Crossover will improve the performance.
Additionally, I occasionally got some weird visual bugs when playing TF2. It looks like plates or boxes of brown/grey popping up from various surfaces. I think it's supposed to be dust from where gunshots are hitting walls/floors but I've also seen it in the spawn zones when no weapons are being fired so I'm not entirely sure what it is.
OS & Software
OS: Ubuntu 6.06.1 LTS (Dapper Drake)
Kernel: 2.6.15-29-386
Filesystem: ext3
KDE: 3.5.5
Crossover: CrossOver Linux Professional 6.2.0 Loki Installer
TF2 Launch Options: -novid -dxlevel 80 -console
Hardware
CPU: AMD Athlon XP 1800+
GPU: Nvidia GeForce FX 5600 (256MB VRAM)
Mobo: Gigabyte GA-7N400 Pro (NForce 2 Ultra 400 chipset)
RAM: 1GB