Triple DES was always just sort of funny to me. "DES is completely broken. So we'll just do it three times in a row now." Well, fun while it lasted, I guess.
DES is weak because it only uses 56 bits, and you can brute force it. 3DES has 168 (56*3) bits with the security of 112 (56*2) bits.
Yes, the problem with 3DES isn't the key length, it's the 64bit block size which opens it up to birthday attacks if it's used in a stream for a long enough with the same key. Defending against this sort of attack is one of the reasons that a lot of VPN setups rekey the encrypted connection with the client at regular intervals. Note that once Gmail disables 3DES it's minimum block size supported will be 128bits.
Biggest reason to avoid DES is the short key. Double-DES doesn't fix that due to the meet-in-the-middle attack. Triple DES "solves" the short key problem.