It seems to me that there are two main kinds of Imperial Guard Players: The Gamer and the Hobbyist.
The Gamer plays games often. He wants to win games, and enjoys the competitive aspects of the game. He has a lot of experience tweaking his army list in order to get the most out of it. The Gamer posts his army lists to the forums to get feedback and advice from other players. He reads tactics articles religiously.
The Hobbyist designs armies, not army lists. He plays games when he can, but usually this is far less frequently than the Gamer. The Hobbyist enjoys the game, but spends far less time playing than he does just thinking about his army. The Hobbyist is more interested in creating an army that fits the background or "makes sense" from a real world perspective. He's interested in fielding a force according to a real world organization, and be damned to its effectiveness on the 40k gaming scene. This "real world perspective" can be simulating a modern force (e.g., my army is theoretically based on a US Army Combined Arms Battalion) or something historical, like a WWII formation, or the Praetorians, simulating the British during the Anglo-Zulu War (q.v. Col. Gravis' fantastic Praetorian Army).
Warhammer 40k is designed as a company-sized game (although you could almost say platoon sized for the more elite armies). For a game of this size, the Gamer might field several armored fist squads, a Leman Russ or two, a Basilisk/Medusa, and a Vendetta. (Or perhaps they'd field the Leafblower list.) There's a little bit of everything, designed to handle many tactical situations. This may be tactically effective within the game, but an organizational nightmare (at least to the more bureaucratic Hobbyist). The Hobbyist is more likely to field something like an infantry company of three platoons of three squads and a weapons section each, with an armor platoon for support. If the Hobbyist were to consider using Vendettas or Valkyries, he would more likely consider using entire platoons of them rather than a singleton--platoons fit better into the TO&E.
The Gamer arms his Command HQ squad with an eye to getting the most damage from it. A typical Gamer Command HQ squad might be armed with an officer with power weapon and plasma pistol, four meltaguns, plasma guns or flamers (4 of each, no mixing), riding in a Chimera.
The Hobbyist may not even consider arming his Colonel with anything more powerful than a laspistol, except maybe a ceremonial power sword. (If he gives his Colonel a power fist, it's probably because his model has one and he wants his army to be WYSIWYG). After all, a Colonel should be commanding his troops. The fighting strength of a regiment is in the arms of the soldiers that make it up, not the commanding officer. His job is to employ the fighting strength of his men, not embody it. His squad would therefore consist of his command staff and liaisons such as a Master-Vox, Master of Ordnance, Officer of the Fleet, bodyguard(s) (aides, rather) and possibly standard bearer, depending on the army style.
The Gamer prowls the forums, reading about other gamers' battles, reading tactics and strategies, and discussing army lists. He will also check out the blogosphere--basically anywhere he can get information on how to improve his game. The purview of the Hobbyist is primarily just the blogosphere--he frequently has his own blog, and discusses painting, modelling, and army organization (as opposed to army lists)
When a new Codex Arrives, the Gamer asks "What new tricks do I have available now? Which units are worth fielding and which aren't?" The Hobbyist asks, "How can I fit the vision of my army into a legal force?"
The Gamer speaks in gamer jargon. He talks about army "builds", refers to other armies by terms such as "Nidzilla, Smurfs, Clown Cars, Lash Armies, Daemon Bombs, and discusses tactics such as "Melta-spam". The names of the armies builds frequently are the same as the primary tactic they use. The Hobbyist speaks in military jargon, and he usually doesn't talk too much about other armies at all. He refers to things like "sections", "detachments", "combined arms", "order of battle", and knows how to spell "ordnance".
After each game, the Hobbyist considers painting on honor badges to the models in his army that performed well. The Gamer considers how to tweak his army list to improve game performance.
The Gamer is more likely to be younger than the Hobbyist. There are plenty of older Gamers, but many players who used to be Gamers got older, got married and started families, and suddenly had much less time to play. When they did have free time, they might only have time to work a little bit on their armies, and suddenly found themselves morphing into Hobbyists.
All in all, there's nothing wrong with either type of player; they are both equally valid ways of being involved in the hobby. I find myself firmly in the category of the "Hobbyist". I consider myself lucky if I get a game in once a month, and when I do, half the time I make my army list the night before, and don't even start thinking about my strategy until game time. Most of the rest of the time I spend painting/converting my guardmen and thinking about their regimental organization. Would I like to play more often? Absolutely...but that'll probably have to wait until my daughter's in college and/or I retire...or win the lottery.
I keep saying to myself that GW would be far better served if they just paid me to play their games. I could then quit my job and do this stuff full time.