Wifi connection (WPA2) is very slow upon login, can take several attempts but usually connects after a minute or so. Connecting to an unsecure network works fine connecting within a second or so after login. My previous Ubuntu 11.10 and 12.04 alpha installations did not have this problem.
driver: iwlwifi
setup: Ubuntu 12.04 beta2 amd64 on a Toshiba Portege R600
uname -a
Linux kuiper 3.2.0-22-generic #35-Ubuntu SMP Tue Apr 3 18:33:15 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
lspci | grep WiFi
01:00.0 Network controller: Intel Corporation WiFi Link 5100
---
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 2.0-0ubuntu4
Architecture: amd64
DistroRelease: Ubuntu 12.04
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=0784f2d3-df81-481d-9014-6fdd04c8ff23
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120301)
MachineType: TOSHIBA PORTEGE R600
Package: linux (not installed)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-22-generic root=UUID=2f94234d-67af-417b-8fd8-9ad23b636dd9 ro quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 3.2.0-22.35-generic 3.2.14
StagingDrivers: mei
Tags: precise staging
Uname: Linux 3.2.0-22-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
dmi.bios.date: 09/04/2009
dmi.bios.vendor: TOSHIBA
dmi.bios.version: Version 3.00
dmi.board.asset.tag: 0000000000
dmi.board.name: Portable PC
dmi.board.vendor: TOSHIBA
dmi.board.version: Version A0
dmi.chassis.asset.tag: 0000000000
dmi.chassis.type: 10
dmi.chassis.vendor: TOSHIBA
dmi.chassis.version: Version 1.0
dmi.modalias: dmi:bvnTOSHIBA:bvrVersion3.00:bd09/04/2009:svnTOSHIBA:pnPORTEGER600:pvrPPR61E-01G00CEN:rvnTOSHIBA:rnPortablePC:rvrVersionA0:cvnTOSHIBA:ct10:cvrVersion1.0:
dmi.product.name: PORTEGE R600
dmi.product.version: PPR61E-01G00CEN
dmi.sys.vendor: TOSHIBA
My laptop has wireless card Intel Centrino Advanced-N 6230 and I had a similar problem on some access points: connection could be established and worked but bitrate would be 1Mb with intermittent packet delays up to 1000ms which made SSH sessions almost unusable.
I tried to build the latest kernel but it did not help much.
However downloading the latest firmware from the official website helped greatly - now uplink speed is reasonably high and stable and packet lag is much lower.
http://