Literę л oddajemy przez: 1) l – przed е, ё, и, ь, ю, я, np. левый – lewyj, лёд – lod, липa – lipa, моль – mol, любой – luboj, Ляля – Lala; 2) ł – przed spółgłoskami, przed samogłoskami а, о, у, ы oraz na końcu wyrazu, np. долгий – dołgij, лaпa – łapa, лоза – łoza, лук – łuk, лысый – łysyj, стол – stoł.
That's from the rules of transcriptio from Russian into Polish.
I've heard my parents' generations pronounce Л as Ł a lot, but what I learned from Russian native speakers is that it's not correct...
As it happens, I attended language classes at work to keep my French and German "up to speed". The French teacher was actually a Polish gentleman who'd lived in the U.K. for a very long time, and I was struck by his pronunciation of "Glasnost" as though it was "Gwasnost" (I knew nothing of Polish at that time, but now realise that he was following the rules you gave above).
My guess is that the transcription rules Jellei mentioned are... a little "outdated". In Polish the formal pronunciation of the letter Ł was different until around mid 20th century and it was actually the same as the Russian Л (the current version exist much longer than that, of course, but it was fully accepted relatively recently). You can still hear it in old audio recordings, and sometimes from old people, especially living in the east.
Today we don't have an equivalent sound in Polish, but we still use Ł in the transcription. Most people will pronounce it wrong as a result, but at least it's still recognizable to experts.