I've been taking it for about 3 years, after various permutations of citalopram and escitalopram ceased working.
I've only occasionally had my BP checked: basically, whenever I've had a dosage increase - I've gone from having lowish BP to highish, but no real cause for concern.
I now take 300mg/daily - I have found it more effective than other things I've tried, though saying that, I'm due to start with lithium as well in 10 days, after the GP sent me back to the psychiatrist as he's the only one licensed to increase the out-patient dose on venlafaxine further...
I stopped completely last September (very bad idea, for reference!) but only realised much afterwards that the symptoms I experienced were withdrawal effects. Basically, I started feeling like I was going to come down with something - shivery and a bit spacey, and my (permanent) vertigo increased. By eyes felt like they were refocussing all the time. It wasn't unutterably vile - just peculiar: but after 6 weeks of no tablets, I realised that I did need them. So they will plan your withdrawal carefully, because of the side effects.
I read the leaflets that come with tablets, but am not big on searching the internet, mainly because there's a lot of nonsense out there. That said, I think a lot of people do experience various side effects - personally, I've suffered with weight gain (though it's hard to know if that's because of the tablets - maybe I'm just eating more because of my state of mind? They certainly don't leave me feeling hungry, and I am horeendous for comfort eating, so I suspect, the more I think of it, that it's me, not Venlafaxine!), vicious insomnia (not being able to get to sleep at all several nights a week) and visual disturbances - it's exacerbated my vertigo a bit, and I'm prone to dizziness. Again, though, those could well be the effects of my chronic insomnia - the healthiest person would get e bit light-headed, I think, after 72 hours without sleep! (Which is why I don't often look on the internet, as I am prone to thinking that every headache is a brain tumour...)
The psychiatrist suggested taking the tablets in the morning -I've tried, but it gives me horrendous nausea, so I'd rather take the insomnia. If you are a breakfast-eater, though, you'd probably be fine to have them in the morning if that suited you better - I have horrible habits, and don't eat until after work in the evenings, and they are not great with an empty stomach.
Remember, this isn't a first line drug, so they won't have prescribed it to you lightly - it's worth a go, though remember also, not everything works for everyone. It's certainly the most effective thing I've tried, having been through various other drugs in the last nine years, as well as during previous episodes - and to me, the side effects are "worth it" because they mean I can keep working full time and stay more-or-less functional and what can pass for "normal"!
The other thing - they have quite a short half-life (or whatever it's called with tablets): it passes out of your system pretty quickly, so if you are later than usual (not minutes, but, say 6 hours or so) taking a tablet, you might well notice - just feeling a bit offish, nothing too grim.
Good luck, though - I hope they work for you!