Definately a boon year for browser vunerabilities.
according to secuna...
Currently there are around thirty uncorrected vunerabilities for Internet Explorer. Around 20 or so have no vendor perscribed work arounds, and out of those 20 maybe a half dozen are above the severe critical and several affect even fully patched WinXP machines with Service Pack 2. At least one of those has the "extremely critical" level, which is the worst rating that Secuna gives out.
With Firefox you have 5 uncorrected vunerabilities with 4 with no work around fix. The highest one is "moderatly critical" which is the 3rd highest level of criticality that secunia perscribes.
There is also a JAVA flaw to worry about, too. There has been found a way to break out of the Java virtual machine sandbox in Sun's stuff so you also have to make sure that everybody is using the latest version of java that is aviable.
All sorts of fun other stuff, like Linux kernel local root exploits other usual crap in Windows.