I'm no expert, but I noticed some video settings combinations that seem to fix a couple of problems. For example, HDR disabled causes the game not to crash on Server Welcome Screen. Upgrading the Kernel to 3.5.0-25 on Ubuntu 12.04 fixes fps random drops (see tutorial bellow). On Ubuntu 13.04 with 310.32 drivers, disabling anti-aliasing fixes fps drop problem.

http://steamcommunity.com/app/221410/discussions/0/864960986991466725/

Processor Information:
Vendor: AuthenticAMD
Speed: 3013 Mhz
2 logical processors
2 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Supported
SSE41: Unsupported
SSE42: Unsupported

Network Information:
Network Speed:

Operating System Version:
Ubuntu Raring Ringtail (development branch) (64 bit)
Kernel Name: Linux
Kernel Version: 3.8.0-9-generic
X Server Vendor: The X.Org Foundation
X Server Release: 11302000
X Window Manager: Compiz
Steam Runtime Version: steam-runtime-release-i386_2013-02-22

Video Card:
Driver: NVIDIA Corporation GeForce 9800 GT/PCIe/SSE2

Driver Version:  3.3.0 NVIDIA 310.32
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 75 Hz
VendorID:  0x10de
DeviceID:  0x614
Number of Monitors:  1
Number of Logical Video Cards:  1
Primary Display Resolution:  1280 x 1024
Desktop Resolution: 1280 x 1024
Primary Display Size: 12,20" x 9,06"  (15,20" diag)
                                        31,0cm x 23,0cm  (38,6cm diag)
Primary Bus: PCI Express 16x
Primary VRAM: 512 MB
Supported MSAA Modes:  2x 4x 8x 16x 

Sound card:
Audio device: VIA VT1705

Memory:
RAM: 3954 Mb

Miscellaneous:
UI Language: English
LANG: en_US.UTF-8
Microphone: Not set
Total Hard Disk Space Available: 253885 Mb
Largest Free Hard Disk Block: 205418 Mb

Installed software:

Recent Failure Reports: